What is vitamin D3, in plain English?

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 I prefer it 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 my 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 I commonly add a separate D3 supplement to reach 2,000 to 4,000 IU daily based on labs. Always confirm the exact dose with your obstetrician or midwife.

Is vitamin D3 safe for infants and children?

Pediatricians routinely prescribe 400 to 600 IU of vitamin D3 daily for breastfed infants and young children, since breast milk does not contain enough on its own. Higher doses should always be guided by a pediatrician using lab values. Liquid drops are easier than capsules for young children.

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 body's stored form. We also check **serum calcium**, **PTH (parathyroid hormone)**, and sometimes **24-hour urine calcium** when running higher doses. These four 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, especially 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, especially 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 we have.

Can vitamin D3 help with autoimmune conditions like Hashimoto's or MS?

Low vitamin D is associated with several autoimmune conditions, and correcting deficiency is part of standard care for Hashimoto's, 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 be a 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. I prefer daily oral D3 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.

What is vitamin D3, in plain English?

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 I prefer it 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 my 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 I commonly add a separate D3 supplement to reach 2,000 to 4,000 IU daily based on labs. Always confirm the exact dose with your obstetrician or midwife.

Is vitamin D3 safe for infants and children?

Pediatricians routinely prescribe 400 to 600 IU of vitamin D3 daily for breastfed infants and young children, since breast milk does not contain enough on its own. Higher doses should always be guided by a pediatrician using lab values. Liquid drops are easier than capsules for young children.

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 body's stored form. We also check serum calcium, PTH (parathyroid hormone), and sometimes 24-hour urine calcium when running higher doses. These four 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, especially 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, especially 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 we have.

Can vitamin D3 help with autoimmune conditions like Hashimoto's or MS?

Low vitamin D is associated with several autoimmune conditions, and correcting deficiency is part of standard care for Hashimoto's, 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 be a 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. I prefer daily oral D3 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.

TL;DR · 30-second take

Vitamin D3 (cholecalciferol) is the active form of vitamin D your skin makes from sunlight and the form most adults should supplement. Most Philadelphians need it from October to April because the sun's angle is too low to make any. The goal is a steady blood level of 50 to 70 ng/mL, paired with vitamin K2 to direct calcium into bones, not arteries.

Vitamin D3 (Cholecalciferol)

The "sunshine hormone" that around 70 percent of Philadelphians are missing.

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

In Philadelphia, vitamin D deficiency is not just a possibility. It is a geographic certainty. Living in Philly means that for nearly six months of the year, our biology is fighting physics. The sun's angle in winter is too low to trigger vitamin D production in the skin, even on a clear day. We have to navigate this geographic reality together to avoid the inevitable winter deficit.

1. Why does the "Drisdol" green capsule (D2) fall short of D3?

If you have ever been flagged for low vitamin D, you were likely prescribed Drisdol (ergocalciferol), the generic 50,000 IU green capsule taken once a week. Here is why we generally avoid this in my practice: Drisdol is vitamin D2, derived from plants and fungi. While D2 is the standard for insurance formularies (the list of drugs your insurance prefers to pay for), it is suboptimal for human physiology.

Poor absorption: D2 has lower affinity for your body's transport proteins than D3 does.
Unstable levels: Because of its shorter half-life (the time it takes to drop by half), weekly dosing creates a "spike and crash" cycle rather than the steady baseline your immune system needs.
The proactive step: If you are currently on the green capsule, this is a conversation worth having. We almost always switch patients to a daily over-the-counter vitamin D3 (cholecalciferol), which is the same form your skin makes naturally.

2. Why do you need vitamin K2 with high-dose vitamin D3?

Vitamin D3 increases the absorption of calcium from your gut. In isolation, that sounds like good news for bone health, but biology is rarely that simple. Without a guide, the newly absorbed calcium does not always end up in your skeleton. It can deposit in soft tissues, arteries, and heart valves, a process called soft tissue calcification. Where vitamin K2 (MK-7) comes in: Think of K2 as the traffic controller for calcium. It activates two key proteins:

Osteocalcin: Pulls calcium into the bone matrix (strengthening the skeleton).
Matrix Gla protein (MGP): Sweeps calcium out of soft tissues and arteries (protecting cardiovascular health).

The strategic pairing: I rarely recommend high-dose D3 (above 5,000 IU per day) without concurrent K2. We want to make sure the calcium we mobilize is directed exactly where it belongs.

⚠ WARNING

Guidance from the Clinic Early in our practice, during time spent in critical care settings, we cared for patients with severe vascular complications. The history often revealed years of high-dose calcium supplementation without the necessary co-factors. It was a stark physiology lesson. Driving calcium into the body without a guide (vitamin K2) does not necessarily strengthen bones. It can inadvertently calcify the arteries. This is why we never look at nutrients in isolation. We generally advise against calcium supplementation without a specific medical indication and strict oversight.

Fishtown Medicine

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

Book a Free 20-Min Call

3. The "Philadelphia Shadow": why local geography forces supplementation

From October to April, Fishtown and the surrounding neighborhoods sit in what we call the "Vitamin D Desert."

The physics: At 40 degrees north latitude, UVB rays (the wavelengths that trigger D3 production in skin) deflect off the atmosphere before they reach us.
The impact: This is essentially a biological winter. We see immune resilience drop, Seasonal Affective Disorder (a form of depression linked to short winter days) spike, and cognitive fog set in.
The solution: Supplementation is not optional here. It is the only reliable way to maintain healthy physiological levels during these months.

4. How should I actually dose vitamin D3?

The goal: A steady, optimized blood level of 50 to 70 ng/mL on the 25-OH vitamin D test.

Maintenance: 2,000 to 5,000 IU daily of D3 (paired with K2).
Correction: If your level is under 30 ng/mL, we may push to 5,000 to 10,000 IU daily for a short window (4 to 8 weeks) to refill the reservoir.
Administration: Vitamin D is fat soluble. Taking it with black coffee on an empty stomach wastes most of the dose. Take it with eggs, avocado, or your largest meal of the day.

5. Agency: when should you be careful with vitamin D3?

Vitamin D acts as a hormone in the body. While safety margins are wide, "more" is not always "better." Hypercalcemia risk (high blood calcium):

If you have sarcoidosis (a condition that causes inflammatory clusters of cells), hyperparathyroidism (overactive parathyroid glands), or a history of kidney stones, do NOT start a high-dose strategy without talking to us first. These conditions change how your body handles calcium and require precise monitoring.

6. Lab considerations

We do not guess. We measure.

The test: 25-OH vitamin D (the storage form, the most reliable marker).
Interpretation:
- Under 30 ng/mL: Deficient (linked with lower immune resilience).
- 30 to 50 ng/mL: "Normal" (standard reference range, but not necessarily optimal).
- 50 to 70 ng/mL: Optimized (where I see the best metabolic and hormonal function).

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

Book Supplement Audit

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.

Still have a question?

He answers personally. Usually within a few hours.