Vitamin D3 (cholecalciferol) is a hormone-like nutrient your skin makes when sunlight hits it, and it is also the form found in animal foods and most quality supplements. It tells your body to absorb calcium, supports immune function, and influences mood. D3 is the same form your body makes naturally, which is why it is preferred over the older prescription D2.

How much vitamin D3 should I take per day?

Most healthy adults in Philadelphia do well on 2,000 to 5,000 IU of vitamin D3 per day, taken with a fat-containing meal. The right dose depends on your starting blood level, body size, sun exposure, and skin tone. We test and adjust rather than guess.

How long does it take for vitamin D3 to raise my blood level?

A meaningful rise in your 25-OH vitamin D level usually takes 8 to 12 weeks of daily dosing. Mood and energy improvements may appear sooner, often within 4 to 6 weeks, but the lab number takes longer to climb. We retest at week 12 before deciding whether to keep, raise, or lower the dose.

Is it better to take vitamin D3 in the morning or at night?

Either time can work, but most patients absorb best when taking it with the largest meal of the day, which is often dinner. Some people report mild sleep disruption with evening dosing, so if your sleep changes, switch to morning. Consistency matters more than time of day.

Should I take vitamin D3 every day or once a week?

Daily dosing of D3 produces the steadiest blood levels, which is what your immune system and bones prefer. The once-weekly 50,000 IU prescription (Drisdol, vitamin D2) creates a spike-and-crash pattern that is less effective and is the wrong form for many people. Daily D3 is the default.

Can I get enough vitamin D from food alone?

Almost no one does. Food sources (fatty fish, egg yolks, fortified milk) deliver only small amounts, often under 200 IU per serving. To match a 2,000 IU dose from food alone, you would need to eat large servings of salmon every day, which is unrealistic for most patients in Philly.

Do I still need vitamin D3 in summer?

In Philadelphia, you can usually pause or lower your D3 dose between June and August if you are outside in shorts and a t-shirt for at least 15 to 20 minutes around midday. Sunscreen, dark skin tone, and indoor jobs all reduce skin synthesis. We test in late summer and again in winter to fine-tune timing.

Should I take vitamin D3 with or without food?

Take vitamin D3 with food, ideally a meal that contains fat (eggs, avocado, olive oil, salmon). Vitamin D is fat-soluble, so taking it on an empty stomach with coffee or water cuts absorption sharply. This is one of the most common "I am taking it but my level is not moving" mistakes.

What is the difference between vitamin D2 and vitamin D3?

Vitamin D3 (cholecalciferol) comes from animal sources or sunlight on skin and matches the form your body makes. Vitamin D2 (ergocalciferol) comes from plants and fungi and is the form in the prescription Drisdol. D3 raises and holds blood levels more reliably, which is why most modern guidelines and physicians prefer it.

Why do I need vitamin K2 with my vitamin D3?

Vitamin D3 increases calcium absorption from food. Vitamin K2 then directs that calcium into bones (where it strengthens the skeleton) instead of arteries (where it causes plaque). Pairing D3 with K2 (specifically MK-7, 100 to 200 mcg per day) is a small step that makes the whole strategy safer and more effective.

Can I take vitamin D3 while pregnant or breastfeeding?

Yes, vitamin D3 is generally considered safe and important during pregnancy and breastfeeding. Most prenatal vitamins contain only 400 to 600 IU, which is often not enough, so a separate D3 supplement is commonly added to reach 2,000 to 4,000 IU daily based on labs. Always confirm the exact dose with your obstetrician or midwife.

What if I have kidney disease? Should I avoid vitamin D3?

People with chronic kidney disease often need vitamin D, but the form and dose require nephrologist input. The kidney converts vitamin D to its active form (calcitriol), and that step is impaired in advanced kidney disease. We never start high-dose D3 in advanced kidney disease without coordinated lab monitoring.

Can high-dose vitamin D3 cause kidney stones?

High-dose vitamin D3 alone does not usually cause kidney stones, but combining high-dose D3 with high-dose calcium supplements can raise urinary calcium and stone risk. People with a personal or family history of stones need careful labs (24-hour urine calcium, serum calcium) before going above 5,000 IU per day. K2 helps direct calcium away from soft tissue but is not a guarantee against stones.

What blood tests should I run to track vitamin D status?

The main test is 25-hydroxyvitamin D (25-OH vitamin D), which measures your bodys stored form. We also check serum calcium, PTH (parathyroid hormone), and sometimes 24-hour urine calcium when running higher doses. These 4 numbers together tell a complete story.

Can vitamin D3 actually help with mood or seasonal depression?

There is reasonable evidence that correcting vitamin D deficiency can ease symptoms of seasonal depression, particularly in northern cities like Philly. The effect is most reliable when starting from a deficient level and reaching the optimized range. Vitamin D3 is not a stand-alone antidepressant, and severe depression still needs proper mental health care.

Does vitamin D3 boost the immune system or prevent colds and flu?

Vitamin D3 supports immune cell function, and meta-analyses suggest a small reduction in respiratory infections, particularly in people who were deficient at baseline. Daily dosing seems to work better than large monthly bolus doses. It is not a magic shield, but maintaining an optimized level is one of the simplest and cheapest immune supports available.

Can vitamin D3 help with autoimmune conditions like Hashimotos or MS?

Low vitamin D is associated with several autoimmune conditions, and correcting deficiency is part of standard care for Hashimotos, multiple sclerosis (MS), and others. Whether high doses meaningfully change disease activity is still being studied. We use vitamin D3 as one supportive layer, not a replacement for the disease-specific treatments your specialist prescribes.

Will vitamin D3 raise my testosterone?

In men with low vitamin D and borderline testosterone, correcting deficiency can produce a small bump in testosterone levels. The change is real but modest. Anyone who hopes vitamin D will substitute for proper sleep, strength training, and a thorough hormone work-up will be disappointed.

How much sun is "enough" sun for a Philadelphian?

Between June and August, around 15 to 20 minutes of midday sun on bare arms and legs (without sunscreen on those areas) several times per week can produce meaningful vitamin D in lighter-skinned adults. People with darker skin tones need significantly more time. Between October and April in Philly, sun exposure produces almost no vitamin D no matter how long you stay outside.

What is the difference between regular D3 and "vegan" D3?

Most D3 supplements are made from lanolin (sheep wool oil). Vegan D3 is typically derived from lichen (a plant-like organism that produces D3 naturally). Both raise blood levels effectively when dosed correctly, so vegans and vegetarians do not need to settle for D2.

How is vitamin D3 different from a vitamin D injection?

Some clinicians give intramuscular vitamin D injections, usually D3 in the 100,000 to 300,000 IU range. The benefit is that injections bypass gut absorption issues and last for months. The downside is that you cannot adjust quickly, and overdosing is harder to reverse. Daily oral D3 is preferred for most patients because it gives finer control.

What does a quality vitamin D3 supplement cost in Philly?

A 6 to 12 month supply of high-quality D3 (often combined with K2 MK-7) usually costs $15 to $40 from third-party tested brands. Insurance does not cover supplements, but the cost is low compared to most prescriptions. The 50,000 IU D2 prescription (Drisdol) often costs more out of pocket than a year of better D3.

Why do dark-skinned and shift-working Philadelphians need more vitamin D?

Melanin (the pigment that gives skin its color) acts as natural sunscreen and reduces vitamin D production by 5 to 10 fold compared to lighter skin. People who work nights, indoors, or who cover most skin for cultural or religious reasons get even less. In Philly, these groups are nearly always deficient by April, and they almost always need supplementation year-round.

Vitamin D3 (cholecalciferol) is a hormone-like nutrient your skin makes when sunlight hits it, and it is also the form found in animal foods and most quality supplements. It tells your body to absorb calcium, supports immune function, and influences mood. D3 is the same form your body makes naturally, which is why it is preferred over the older prescription D2.

How much vitamin D3 should I take per day?

Most healthy adults in Philadelphia do well on 2,000 to 5,000 IU of vitamin D3 per day, taken with a fat-containing meal. The right dose depends on your starting blood level, body size, sun exposure, and skin tone. We test and adjust rather than guess.

How long does it take for vitamin D3 to raise my blood level?

A meaningful rise in your 25-OH vitamin D level usually takes 8 to 12 weeks of daily dosing. Mood and energy improvements may appear sooner, often within 4 to 6 weeks, but the lab number takes longer to climb. We retest at week 12 before deciding whether to keep, raise, or lower the dose.

Is it better to take vitamin D3 in the morning or at night?

Either time can work, but most patients absorb best when taking it with the largest meal of the day, which is often dinner. Some people report mild sleep disruption with evening dosing, so if your sleep changes, switch to morning. Consistency matters more than time of day.

Should I take vitamin D3 every day or once a week?

Daily dosing of D3 produces the steadiest blood levels, which is what your immune system and bones prefer. The once-weekly 50,000 IU prescription (Drisdol, vitamin D2) creates a spike-and-crash pattern that is less effective and is the wrong form for many people. Daily D3 is the default.

Can I get enough vitamin D from food alone?

Almost no one does. Food sources (fatty fish, egg yolks, fortified milk) deliver only small amounts, often under 200 IU per serving. To match a 2,000 IU dose from food alone, you would need to eat large servings of salmon every day, which is unrealistic for most patients in Philly.

Do I still need vitamin D3 in summer?

In Philadelphia, you can usually pause or lower your D3 dose between June and August if you are outside in shorts and a t-shirt for at least 15 to 20 minutes around midday. Sunscreen, dark skin tone, and indoor jobs all reduce skin synthesis. We test in late summer and again in winter to fine-tune timing.

Should I take vitamin D3 with or without food?

Take vitamin D3 with food, ideally a meal that contains fat (eggs, avocado, olive oil, salmon). Vitamin D is fat-soluble, so taking it on an empty stomach with coffee or water cuts absorption sharply. This is one of the most common "I am taking it but my level is not moving" mistakes.

What is the difference between vitamin D2 and vitamin D3?

Vitamin D3 (cholecalciferol) comes from animal sources or sunlight on skin and matches the form your body makes. Vitamin D2 (ergocalciferol) comes from plants and fungi and is the form in the prescription Drisdol. D3 raises and holds blood levels more reliably, which is why most modern guidelines and physicians prefer it.

Why do I need vitamin K2 with my vitamin D3?

Vitamin D3 increases calcium absorption from food. Vitamin K2 then directs that calcium into bones (where it strengthens the skeleton) instead of arteries (where it causes plaque). Pairing D3 with K2 (specifically MK-7, 100 to 200 mcg per day) is a small step that makes the whole strategy safer and more effective.

Can I take vitamin D3 while pregnant or breastfeeding?

Yes, vitamin D3 is generally considered safe and important during pregnancy and breastfeeding. Most prenatal vitamins contain only 400 to 600 IU, which is often not enough, so a separate D3 supplement is commonly added to reach 2,000 to 4,000 IU daily based on labs. Always confirm the exact dose with your obstetrician or midwife.

What if I have kidney disease? Should I avoid vitamin D3?

People with chronic kidney disease often need vitamin D, but the form and dose require nephrologist input. The kidney converts vitamin D to its active form (calcitriol), and that step is impaired in advanced kidney disease. We never start high-dose D3 in advanced kidney disease without coordinated lab monitoring.

Can high-dose vitamin D3 cause kidney stones?

High-dose vitamin D3 alone does not usually cause kidney stones, but combining high-dose D3 with high-dose calcium supplements can raise urinary calcium and stone risk. People with a personal or family history of stones need careful labs (24-hour urine calcium, serum calcium) before going above 5,000 IU per day. K2 helps direct calcium away from soft tissue but is not a guarantee against stones.

What blood tests should I run to track vitamin D status?

The main test is 25-hydroxyvitamin D (25-OH vitamin D), which measures your bodys stored form. We also check serum calcium, PTH (parathyroid hormone), and sometimes 24-hour urine calcium when running higher doses. These 4 numbers together tell a complete story.

Can vitamin D3 actually help with mood or seasonal depression?

There is reasonable evidence that correcting vitamin D deficiency can ease symptoms of seasonal depression, particularly in northern cities like Philly. The effect is most reliable when starting from a deficient level and reaching the optimized range. Vitamin D3 is not a stand-alone antidepressant, and severe depression still needs proper mental health care.

Does vitamin D3 boost the immune system or prevent colds and flu?

Vitamin D3 supports immune cell function, and meta-analyses suggest a small reduction in respiratory infections, particularly in people who were deficient at baseline. Daily dosing seems to work better than large monthly bolus doses. It is not a magic shield, but maintaining an optimized level is one of the simplest and cheapest immune supports available.

Can vitamin D3 help with autoimmune conditions like Hashimotos or MS?

Low vitamin D is associated with several autoimmune conditions, and correcting deficiency is part of standard care for Hashimotos, multiple sclerosis (MS), and others. Whether high doses meaningfully change disease activity is still being studied. We use vitamin D3 as one supportive layer, not a replacement for the disease-specific treatments your specialist prescribes.

Will vitamin D3 raise my testosterone?

In men with low vitamin D and borderline testosterone, correcting deficiency can produce a small bump in testosterone levels. The change is real but modest. Anyone who hopes vitamin D will substitute for proper sleep, strength training, and a thorough hormone work-up will be disappointed.

How much sun is "enough" sun for a Philadelphian?

Between June and August, around 15 to 20 minutes of midday sun on bare arms and legs (without sunscreen on those areas) several times per week can produce meaningful vitamin D in lighter-skinned adults. People with darker skin tones need significantly more time. Between October and April in Philly, sun exposure produces almost no vitamin D no matter how long you stay outside.

What is the difference between regular D3 and "vegan" D3?

Most D3 supplements are made from lanolin (sheep wool oil). Vegan D3 is typically derived from lichen (a plant-like organism that produces D3 naturally). Both raise blood levels effectively when dosed correctly, so vegans and vegetarians do not need to settle for D2.

How is vitamin D3 different from a vitamin D injection?

Some clinicians give intramuscular vitamin D injections, usually D3 in the 100,000 to 300,000 IU range. The benefit is that injections bypass gut absorption issues and last for months. The downside is that you cannot adjust quickly, and overdosing is harder to reverse. Daily oral D3 is preferred for most patients because it gives finer control.

What does a quality vitamin D3 supplement cost in Philly?

A 6 to 12 month supply of high-quality D3 (often combined with K2 MK-7) usually costs $15 to $40 from third-party tested brands. Insurance does not cover supplements, but the cost is low compared to most prescriptions. The 50,000 IU D2 prescription (Drisdol) often costs more out of pocket than a year of better D3.

Why do dark-skinned and shift-working Philadelphians need more vitamin D?

Melanin (the pigment that gives skin its color) acts as natural sunscreen and reduces vitamin D production by 5 to 10 fold compared to lighter skin. People who work nights, indoors, or who cover most skin for cultural or religious reasons get even less. In Philly, these groups are nearly always deficient by April, and they almost always need supplementation year-round.

Vitamin D3 Clinical Guide: The "Drisdol" Trap

TL;DR30-second take

Vitamin D3 (cholecalciferol) is the hormone-like nutrient your skin makes from sunlight, and the form most adults in Philadelphia need to supplement from October to April because latitude blocks UVB production entirely. Target a 25-OH vitamin D blood level of 50 to 70 ng/mL, achieved with 2,000 to 5,000 IU of D3 daily taken with a fat-containing meal. Pair any dose above 5,000 IU with vitamin K2 (MK-7) to direct calcium into bones, not arteries. If you have sarcoidosis, hyperparathyroidism, or a history of kidney stones, do not start high-dose D3 without a physician guiding the labs.

In Philadelphia, vitamin D deficiency is not just a possibility. It is a geographic certainty. For nearly 6 months of the year, our biology is fighting physics: the suns angle in winter is too low to trigger vitamin D production in the skin, even on a clear day.

Get the right form (D3), not the cheap form (D2).

What vitamin D3 is and what it does

Vitamin D3 (cholecalciferol) is a hormone-like nutrient your skin makes when sunlight hits it. After absorption, your liver and kidneys convert it to calcitriol, its active form, which then regulates calcium absorption from the gut, supports immune cell signaling, influences mood, and governs bone metabolism.

Most people associate vitamin D with bone health, and that is fair, but the biology goes much further. Vitamin D receptors sit on immune cells, muscle cells, and neurons. Correcting a deficiency touches immune resilience, mood, cognitive clarity, and muscle strength all at once.

The prescription form you may have been handed, Drisdol (ergocalciferol, vitamin D2), is a plant-derived version that has a lower affinity for your bodys transport proteins and a shorter half-life than D3. Weekly 50,000 IU doses of D2 create a spike-and-crash cycle rather than the steady baseline your immune system needs. We almost always switch patients to daily over-the-counter vitamin D3, which is the same form your skin makes naturally.

Who this is for (and who it isnt)

Vitamin D3 supplementation fits almost every adult in Philadelphia, but the dose and pairing depend on context.

It tends to fit:

Most Philadelphians from October to April. At 40 degrees north latitude, UVB rays deflect off the atmosphere before reaching us all winter. Supplementation is not optional here; it is the only reliable way to maintain healthy levels.
People with darker skin tones or shift-working schedules. Melanin reduces vitamin D production by 5 to 10 fold compared to lighter skin. People who work nights or indoors get even less sun exposure and are nearly always deficient by April.
Anyone on 2,000 IU or more daily. At these doses, pairing with vitamin K2 (MK-7, 100 to 200 mcg per day) is important to direct calcium into bones and away from arteries.
People on medications that lower D levels, including seizure medications (phenytoin, phenobarbital), long-term corticosteroids (prednisone), and fat-absorption blockers (orlistat).

It is not the right first move, or it needs a careful conversation first, if:

You have sarcoidosis, hyperparathyroidism, or a history of kidney stones. These conditions change how your body handles calcium, and high-dose D3 can worsen hypercalcemia.
You have advanced chronic kidney disease. The kidneys convert D3 to its active form (calcitriol), and that step is impaired. A nephrologist needs to guide the form and dose.
You are taking thiazide diuretics. These blood pressure medications can raise calcium levels when combined with vitamin D, so we monitor labs carefully.

How we evaluate it: safety, then effectiveness, then cost

Every supplement we recommend runs the same 3 gates, in order (we go deep on this in how we choose supplements).

Safety first. We want a third-party-tested product (NSF, USP, or ConsumerLab) free of contaminants and accurately dosed. We also want the safe pairing confirmed: high-dose D3 without K2 leaves newly absorbed calcium without direction, and it can land in arteries and soft tissue. The co-factor is not optional above 5,000 IU.
Effectiveness second. Form matters enormously. Cholecalciferol (D3) raises and holds blood levels more reliably than ergocalciferol (D2) per IU. We dose to a lab target, 50 to 70 ng/mL on the 25-OH vitamin D test, rather than guessing by body weight alone.
Cost last. A 6 to 12 month supply of high-quality D3 paired with K2 MK-7 usually costs $15 to $40 from third-party tested brands. That is low compared to most prescriptions. The 50,000 IU D2 Drisdol prescription often costs more out of pocket than a year of better D3.

How to dose it, and when

The goal is a steady blood level of 50 to 70 ng/mL on the 25-OH vitamin D test. We test and adjust rather than guess.

Maintenance: 2,000 to 5,000 IU of D3 daily, paired with K2 MK-7.
Correction: If your level is under 30 ng/mL, we may push to 5,000 to 10,000 IU daily for 4 to 8 weeks to refill the reservoir, then step back down.
Take it with fat. Vitamin D is fat-soluble. Taking it with black coffee on an empty stomach wastes most of the dose. With eggs, avocado, olive oil, or your largest meal of the day, absorption is reliable.
Morning vs. evening. Either time can work. Some patients report mild sleep disruption with evening dosing. If your sleep changes, switch to morning. Consistency matters more than time of day.

What to expect on the timeline: mood and energy improvements sometimes appear within 4 to 6 weeks, but your 25-OH vitamin D lab number usually takes 8 to 12 weeks of daily dosing to climb meaningfully. We retest at week 12 before deciding whether to keep, raise, or lower the dose.

From June to August in Philadelphia, 15 to 20 minutes of midday sun on bare arms and legs several times per week can produce meaningful vitamin D in lighter-skinned adults. Darker skin, sunscreen, and indoor jobs all reduce synthesis. We test in late summer and again in winter to fine-tune timing.

What vitamin D3 does (and does not do) for stroke

This is one of the cleanest examples of where observational data and randomized data tell different stories, and the resolution matters for how we use D3.

Fishtown Medicine

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Start your intake

Observational signal: UK Biobank data show severe vitamin D deficiency (< 25 nmol/L, or about 10 ng/mL) is associated with a 40% higher stroke risk (HR 1.40).
RCT signal: The VITAL trial (n = 25,871; D3 2,000 IU/day vs. placebo over 5.3 years) showed no reduction in cardiovascular events or stroke, even in participants with baseline 25(OH)D below 20 ng/mL.
Genetic signal: Mendelian randomization analysis from the same UK Biobank dataset did not support a causal link for stroke (in contrast to dementia, where causation is confirmed).

The clinical version: low vitamin D tracks with stroke risk but does not appear to drive it. The observational association is most likely confounding by overall health, mobility, time outdoors, and dietary quality. We still test and replete documented deficiency for bone, immune, and dementia-prevention reasons, but we do not chase a higher 25(OH)D specifically for stroke risk reduction.

For the broader supplement framework in stroke prevention, see the Stroke Prevention guide.

Flaws, side effects, and interactions

No supplement is perfect, and being honest about the downsides is part of the job.

Hypercalcemia risk. High-dose D3 raises calcium absorption. If calcium has nowhere to go because K2 is missing, it can deposit in soft tissue, arteries, and heart valves. We pair D3 with K2 above 5,000 IU and monitor serum calcium.
Medication interactions. Seizure medications, long-term steroids, and orlistat lower vitamin D levels and may require higher doses to compensate. Thiazide diuretics can raise calcium when combined with D3. Always report your full medication list.
Kidney stone risk at high doses. High-dose D3 combined with high-dose calcium supplements can raise urinary calcium and stone risk. People with a history of stones need 24-hour urine calcium and serum calcium labs before going above 5,000 IU daily.
Vitamin D toxicity. Toxicity is rare but real, usually from very high doses taken without testing. Levels above 100 ng/mL warrant stopping or reducing the dose and rechecking calcium. Symptoms include nausea, weakness, and kidney stress.
The D2 trap. The prescription Drisdol (D2) creates a spike-and-crash cycle with weekly dosing and is less effective per IU than D3. If you are on it, that is a conversation worth having at your next visit.

We look for: cholecalciferol (D3, not D2), third-party testing (NSF, USP, or ConsumerLab), and a K2 MK-7 partner at 100 to 200 mcg per day when doses exceed 2,000 IU.
Worth considering: combination D3 plus K2 capsules in a single product simplify dosing and reduce the chance of forgetting one half of the pair. Many quality brands offer this.
Vegan D3: most D3 is made from lanolin (sheep wool oil). Vegan D3 is typically derived from lichen and raises blood levels just as effectively when dosed correctly. Vegans do not need to settle for D2.
We dont lean on: the Drisdol green capsule as a long-term solution, doses above 10,000 IU daily without physician supervision, or calcium supplements added on top without a specific medical indication and careful lab oversight.

Guidance from the Clinic

"Early in my practice, I cared for patients with serious vascular complications, and the history often showed years of high-dose calcium without the right co-factors. That was a sharp physiology lesson. Vitamin D3 drives calcium in, and K2 is the guide that tells it where to go. We never look at these nutrients in isolation. Test first, pair D3 with K2, take it with food that has fat, and recheck at 12 weeks. That is the whole protocol."

Dr. Ash

Actionable Steps

Get your vitamin D working, not just in range.

Test your 25-OH vitamin D first. Know your starting number before picking a dose. Under 30 ng/mL is deficient; 50 to 70 ng/mL is the optimized target.
Choose D3, not D2. Cholecalciferol (D3) is the form your skin makes and the form that raises levels reliably. Skip ergocalciferol (D2, Drisdol).
Pair with K2 MK-7. Add 100 to 200 mcg of K2 MK-7 daily whenever your D3 dose is 2,000 IU or more.
Take it with fat. Eggs, avocado, olive oil, or any fat-containing meal. Never on an empty stomach.
Retest at 12 weeks. Adjust to land in the 50 to 70 ng/mL range, then check again seasonally.

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Key Takeaways

Vitamin D3 (cholecalciferol) is the form your body makes from sunlight and the form that raises blood levels reliably; Drisdol (D2) is less effective per IU.
Most Philadelphians need D3 supplementation from October to April because latitude blocks UVB production entirely during those months.
Target 50 to 70 ng/mL on the 25-OH vitamin D test; maintenance dose is 2,000 to 5,000 IU daily taken with a fat-containing meal.
Pair any dose above 2,000 IU with vitamin K2 MK-7 (100 to 200 mcg) to direct calcium into bones, not arteries.
People with sarcoidosis, hyperparathyroidism, kidney stones, or advanced kidney disease need physician-guided labs before starting high-dose D3.

Scientific References

Holick, M. F., et al. (2011). Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism, 96(7), 1911-1930.
Tripkovic, L., et al. (2012). Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. American Journal of Clinical Nutrition, 95(6), 1357-1364.
Knapen, M. H. J., et al. (2013). Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporosis International, 24(9), 2499-2507.
Martineau, A. R., et al. (2017). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ, 356, i6583.

Fishtown Medicine | Articles

2418 E York St, Philadelphia, PA 19125(267) 360-7927 hello@fishtownmedicine.comHSA/FSA Eligible

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Frequently Asked Questions

Common Questions

Deep-Dive Questions

Several medications can lower vitamin D levels or change how it is processed, including some seizure medications (phenytoin, phenobarbital), corticosteroids (long-term prednisone), and weight-loss drugs that block fat absorption (orlistat). Thiazide diuretics (a type of blood pressure medication) can raise calcium levels when combined with vitamin D, so we monitor labs carefully. Tell us about every prescription before adjusting your dose.

Ready when you are

Start your intake

Dr. Ash reads every intake himself, and answers questions personally - usually within a few hours.

TL;DR30-second take

Get the right form (D3), not the cheap form (D2).

What vitamin D3 is and what it does

Who this is for (and who it isnt)

Vitamin D3 supplementation fits almost every adult in Philadelphia, but the dose and pairing depend on context.

It tends to fit:

Most Philadelphians from October to April. At 40 degrees north latitude, UVB rays deflect off the atmosphere before reaching us all winter. Supplementation is not optional here; it is the only reliable way to maintain healthy levels.
People with darker skin tones or shift-working schedules. Melanin reduces vitamin D production by 5 to 10 fold compared to lighter skin. People who work nights or indoors get even less sun exposure and are nearly always deficient by April.
Anyone on 2,000 IU or more daily. At these doses, pairing with vitamin K2 (MK-7, 100 to 200 mcg per day) is important to direct calcium into bones and away from arteries.
People on medications that lower D levels, including seizure medications (phenytoin, phenobarbital), long-term corticosteroids (prednisone), and fat-absorption blockers (orlistat).

It is not the right first move, or it needs a careful conversation first, if:

You have sarcoidosis, hyperparathyroidism, or a history of kidney stones. These conditions change how your body handles calcium, and high-dose D3 can worsen hypercalcemia.
You have advanced chronic kidney disease. The kidneys convert D3 to its active form (calcitriol), and that step is impaired. A nephrologist needs to guide the form and dose.
You are taking thiazide diuretics. These blood pressure medications can raise calcium levels when combined with vitamin D, so we monitor labs carefully.

How we evaluate it: safety, then effectiveness, then cost

Every supplement we recommend runs the same 3 gates, in order (we go deep on this in how we choose supplements).

Safety first. We want a third-party-tested product (NSF, USP, or ConsumerLab) free of contaminants and accurately dosed. We also want the safe pairing confirmed: high-dose D3 without K2 leaves newly absorbed calcium without direction, and it can land in arteries and soft tissue. The co-factor is not optional above 5,000 IU.
Effectiveness second. Form matters enormously. Cholecalciferol (D3) raises and holds blood levels more reliably than ergocalciferol (D2) per IU. We dose to a lab target, 50 to 70 ng/mL on the 25-OH vitamin D test, rather than guessing by body weight alone.
Cost last. A 6 to 12 month supply of high-quality D3 paired with K2 MK-7 usually costs $15 to $40 from third-party tested brands. That is low compared to most prescriptions. The 50,000 IU D2 Drisdol prescription often costs more out of pocket than a year of better D3.

How to dose it, and when

The goal is a steady blood level of 50 to 70 ng/mL on the 25-OH vitamin D test. We test and adjust rather than guess.

Maintenance: 2,000 to 5,000 IU of D3 daily, paired with K2 MK-7.
Correction: If your level is under 30 ng/mL, we may push to 5,000 to 10,000 IU daily for 4 to 8 weeks to refill the reservoir, then step back down.
Take it with fat. Vitamin D is fat-soluble. Taking it with black coffee on an empty stomach wastes most of the dose. With eggs, avocado, olive oil, or your largest meal of the day, absorption is reliable.
Morning vs. evening. Either time can work. Some patients report mild sleep disruption with evening dosing. If your sleep changes, switch to morning. Consistency matters more than time of day.

What vitamin D3 does (and does not do) for stroke

This is one of the cleanest examples of where observational data and randomized data tell different stories, and the resolution matters for how we use D3.

Fishtown Medicine

A 90-minute conversation with Dr. Ash. A written plan you can actually follow.

Start your intake

Observational signal: UK Biobank data show severe vitamin D deficiency (< 25 nmol/L, or about 10 ng/mL) is associated with a 40% higher stroke risk (HR 1.40).
RCT signal: The VITAL trial (n = 25,871; D3 2,000 IU/day vs. placebo over 5.3 years) showed no reduction in cardiovascular events or stroke, even in participants with baseline 25(OH)D below 20 ng/mL.
Genetic signal: Mendelian randomization analysis from the same UK Biobank dataset did not support a causal link for stroke (in contrast to dementia, where causation is confirmed).

For the broader supplement framework in stroke prevention, see the Stroke Prevention guide.

Flaws, side effects, and interactions

No supplement is perfect, and being honest about the downsides is part of the job.

Hypercalcemia risk. High-dose D3 raises calcium absorption. If calcium has nowhere to go because K2 is missing, it can deposit in soft tissue, arteries, and heart valves. We pair D3 with K2 above 5,000 IU and monitor serum calcium.
Medication interactions. Seizure medications, long-term steroids, and orlistat lower vitamin D levels and may require higher doses to compensate. Thiazide diuretics can raise calcium when combined with D3. Always report your full medication list.
Kidney stone risk at high doses. High-dose D3 combined with high-dose calcium supplements can raise urinary calcium and stone risk. People with a history of stones need 24-hour urine calcium and serum calcium labs before going above 5,000 IU daily.
Vitamin D toxicity. Toxicity is rare but real, usually from very high doses taken without testing. Levels above 100 ng/mL warrant stopping or reducing the dose and rechecking calcium. Symptoms include nausea, weakness, and kidney stress.
The D2 trap. The prescription Drisdol (D2) creates a spike-and-crash cycle with weekly dosing and is less effective per IU than D3. If you are on it, that is a conversation worth having at your next visit.

We look for: cholecalciferol (D3, not D2), third-party testing (NSF, USP, or ConsumerLab), and a K2 MK-7 partner at 100 to 200 mcg per day when doses exceed 2,000 IU.
Worth considering: combination D3 plus K2 capsules in a single product simplify dosing and reduce the chance of forgetting one half of the pair. Many quality brands offer this.
Vegan D3: most D3 is made from lanolin (sheep wool oil). Vegan D3 is typically derived from lichen and raises blood levels just as effectively when dosed correctly. Vegans do not need to settle for D2.
We dont lean on: the Drisdol green capsule as a long-term solution, doses above 10,000 IU daily without physician supervision, or calcium supplements added on top without a specific medical indication and careful lab oversight.

Guidance from the Clinic

"Early in my practice, I cared for patients with serious vascular complications, and the history often showed years of high-dose calcium without the right co-factors. That was a sharp physiology lesson. Vitamin D3 drives calcium in, and K2 is the guide that tells it where to go. We never look at these nutrients in isolation. Test first, pair D3 with K2, take it with food that has fat, and recheck at 12 weeks. That is the whole protocol."

Dr. Ash

Actionable Steps

Get your vitamin D working, not just in range.

Test your 25-OH vitamin D first. Know your starting number before picking a dose. Under 30 ng/mL is deficient; 50 to 70 ng/mL is the optimized target.
Choose D3, not D2. Cholecalciferol (D3) is the form your skin makes and the form that raises levels reliably. Skip ergocalciferol (D2, Drisdol).
Pair with K2 MK-7. Add 100 to 200 mcg of K2 MK-7 daily whenever your D3 dose is 2,000 IU or more.
Take it with fat. Eggs, avocado, olive oil, or any fat-containing meal. Never on an empty stomach.
Retest at 12 weeks. Adjust to land in the 50 to 70 ng/mL range, then check again seasonally.

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Key Takeaways

Vitamin D3 (cholecalciferol) is the form your body makes from sunlight and the form that raises blood levels reliably; Drisdol (D2) is less effective per IU.
Most Philadelphians need D3 supplementation from October to April because latitude blocks UVB production entirely during those months.
Target 50 to 70 ng/mL on the 25-OH vitamin D test; maintenance dose is 2,000 to 5,000 IU daily taken with a fat-containing meal.
Pair any dose above 2,000 IU with vitamin K2 MK-7 (100 to 200 mcg) to direct calcium into bones, not arteries.
People with sarcoidosis, hyperparathyroidism, kidney stones, or advanced kidney disease need physician-guided labs before starting high-dose D3.