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Vitamin D

Vitamin D is a fat-soluble essential vitamin that our skin synthesizes when exposed to the sun. It benefits us in many ways, from bone health to mood.

Our evidence-based analysis on vitamin d features 458 unique references to scientific papers.

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Summary of Vitamin D

Primary Information, Benefits, Effects, and Important Facts

Vitamin D is a fat-soluble nutrient. It is one of the 24 micronutrients critical for human survival. The sun is the major natural source of the nutrient, but vitamin D is also found naturally in fish and eggs. It is also added to dairy products.

Supplemental vitamin D is associated with a wide range of benefits, including increased cognition, immune health, bone health and well-being. Supplementation can also reduce the risks of cancer, heart disease, diabetes and multiple sclerosis. People deficient in vitamin D may also experience increased testosterone levels after supplementation.

The body produces vitamin D from cholesterol, provided there is an adequate amount of UV light from sun exposure. There is only a sufficient amount of UV light coming from the sun when the UV index is 3 or higher, which only occurs year-round near the equator, between the 37th parallels.

Most people are not deficient in vitamin D, but they do not have an optimal level of vitamin D either. Due to the many health benefits of vitamin D, supplementation is encouraged if optimal levels are not present in the body.

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How to Take

Medical Disclaimer

Recommended dosage, active amounts, other details

The recommended daily allowance for Vitamin D is currently set at 400-800IU/day, but this is too low for adults. The safe upper limit in the United States and Canada is 4,000IU/day. Research suggests that the true safe upper limit is 10,000IU/day. For moderate supplementation, a 1,000-2,000IU dose of vitamin D3 is sufficient to meet the needs of most of the population. This is the lowest effective dose range. Higher doses, based on body weight, are in the range of 20-80IU/kg daily.

Vitamin D3 supplementation (cholecalciferol) is recommended over D2 supplementation (ergocalciferol), since D3 is used more effectively in the body.

Vitamin D should be taken daily, with meals or a source of fat, like fish oil.

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Human Effect Matrix

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what effects vitamin d has on your body, and how strong these effects are.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-a Notable Moderate See all 4 studies
The risk of falls in the elderly (and subsequently, rate of bone fractures) appears to be significantly reduced with Vitamin D supplementation at 700 IU or greater, with most research in the 700-1000 IU range. Lower doses do not appear effective, and a greater protective effect appears to exist alongside calcium supplementation (and possibly Vitamin K supplementation)
grade-a Minor Moderate See all 4 studies
There appears to be less risk of cardiovascular disease and related cardiovascular complications with supplementation of 1,000 IU of Vitamin D or higher serum levels of Vitamin D, although studies using less have had null results. The degree of prevention found in positive trials is of borderline clinical significance.
grade-b Strong Very High See all 4 studies
Vitamin D supplementation is the reference drug for reductions in parathyroid hormone due to directly negatively regulating its secretion
grade-b Notable - See study
The association between serum Vitamin D at 37ng/mL and colorectal cancer is is approximately a halving of risk according to one meta-analysis, which is a notable risk reduction
grade-b Minor Very High See all 3 studies
Some correlational and intervention studies note that higher serum vitamin D is associated with mildly lower blood pressure, although the evidence is somewhat conflicted and effects that have been found are rather small.
grade-b Minor - See study
A decrease in bone fracture risk (nonvetebral and hip) appears to exist when supplemental doses of Vitamin D3 are taken above 800 IU, with this protective effect being highly correlated with the improvement in functionality and fall reduction risk
grade-b Minor Low See all 3 studies
Mixed effects on overweight/obese persons, but it appears that normalizing a deficiency may aid fat loss in persons of higher body weight. Insufficient evidence to suggest the role of Vitamin D in lean persons
grade-c Notable - See study
An improvement in muscular and neural functionality in the elderly is thought to underlie the reductions of fall risk and reduced bone fracture rate seen in elderly cohorts
grade-c Minor Very High See 2 studies
Cohorts of people with higher serum Vitamin D appear to die less frequently than cohorts with less serum Vitamin D; this may be heavily influenced by reducing falls in the elderly (reduction of falls and subsequent hospitalizations reducing death rates)
grade-c Minor - See study
Appears to be somewhat effective at reducing the occurrence of asthma attacks in youth
grade-c Minor - See study
A higher vitamin D level in serum during growth spurts in children is associated with greater heights during adulthood; currently no evidence to support the role of Vitamin D in inducing height growth in adults
grade-c Minor Very High See 2 studies
May reduce the risk of catching the flu
grade-c Minor Very High See all 3 studies
An improvement in insulin secretion is noted in diabetics (type II mostly) and in persons at risk for diabetes, which is thought to be secondary to protective effects at the level of the pancreas.
grade-c Minor Moderate See all 4 studies
Improvements in insulin sensitivity can occur secondary to increasing pancreatic insulin secretion
grade-c Minor - See study
An increase in IL-5 has been noted with Vitamin D supplementation
grade-c Minor Very High See 2 studies
Either no significant influence on LDL cholesterol or a slight increase (around 5%) has been noted; practical significance of this information unknown
- See 2 studies
An increase in lean mass has been noted in dieting obese women relative to control (2,000IU) and a trend to reduce lean mass relative to control has been noted in exercising healthy persons (4,000IU); there appears to be potential for both effects with Vitamin D supplementation, but there is insufficient evidence to draw conclusions
grade-c Minor Very High See all 5 studies
Most studies have found a decrease in general symptoms when given to women with vitamin D deficiency, some finding notable reductions and some finding small reductions. It's currently not known why studies differ, and more research is needed.
grade-c Minor - See study
Inflammatory symptoms associated with Lupus appear to be reduced with Vitamin D ingestion
grade-c Minor - See study
A decrease in symptoms associated with tuberculosis are noted with Vitamin D
grade-c Minor - See study
A decrease has been noted over time relative to placebo, of relatively minor magnitude
grade-c Minor - See study
An increase in testosterone has been noted in men with 3,332 IU of Vitamin D over the course of a year
grade-c Minor - See study
The decrease in triglycerides is present after long term ingestion of Vitamin D, although it isn't to a highly significant degree
grade-c - - See study
No significant influence on fasting blood glucose levels
grade-c - - See study
grade-c - - See study
Superloading Vitamin D (rather than staying sufficient) does not appear to further increase absorption rates of calcium, although normalizing a deficiency can aid in absorption which is hindered.
grade-c - - See study
grade-c - - See study
No significant influence on endothelial function
grade-c - - See study
No significant alterations in food intake noted with Vitamin D supplementation
grade-c - Very High See 2 studies
The decrease in HbA1c is statistically insignificant and very small in magnitude, likely not a concern.
grade-c - - See study
grade-c - - See study
No significant influence on select inflammatory cytokines
grade-c - Very High See 2 studies
No significant influence on fasting insulin levels
grade-c - - See study
No detectable influence on metabolic rate over time
grade-c - - See study
grade-c - Very High See 2 studies
Although a trend to increase power output has been noted, most research suggest no benefit, although recovery times may improve.
grade-c - - See study
grade-c - - See study
Lack of efficacy in reducing rate of sickness
grade-c - Very High See 2 studies
No significant alterations noted in weight, even when fat mass is lost, in obese persons
grade-d Notable - See study
The risk of developing MS is significantly reduced by both sunlight, latitude, and supplemental Vitamin D
grade-d Minor Very High See 2 studies
May reduce symptoms of athralgia
grade-d Minor Very High See 2 studies
There is less risk of breast cancer associated with Vitamin D supplementation
grade-d Minor - See study
There was a small reduction in the rate and severity of menstrual cramps from 50,000 IU weekly in vitamin D deficient girls. More research is needed.
grade-d Minor - See study
Small drops in hematocrit were noted in vitamin D-insufficient healthy people supplemented with 800 IU over 12 weeks.
grade-d Minor - See study
Small drops in hemoglobin were noted in vitamin D-insufficient healthy people supplemented with 800 IU over 12 weeks.
grade-d Minor - See study
May reduce the incidence of type 1 diabetes in offspring and adults when supplemented (for the former, but the mothers)
grade-d Minor - See study
Appears to be associated with less risk of pancreatic cancer
grade-d Minor - See study
Small drops in red blood cell count were noted in vitamin D-insufficient healthy people supplemented with 800 IU over 12 weeks.
grade-d Minor - See study
There appears to be a lower relapse rate in multiple sclerosis patients when Vitamin D is present at higher concentrations
grade-d - -
grade-d - - See study
grade-d - - See all 3 studies
grade-d Very High See 2 studies
One randomized, controlled trial in 40 depressed patients found a modest but non-significant (p=0.06) reduction in Beck-II score compared with placebo after supplementation of 50,000 IU of vitamin D once at the start of an 8 week period.
grade-d - - See 2 studies
grade-d - - See study
grade-d - - See study
No change in HDL-C was seen in vitamin D-insufficient healthy people supplemented with 800 IU over 12 weeks.
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study

Studies Excluded from Consideration

  • Used injections of the active hormone[1]

  • Confounded with calcium [2]

Frequently Asked Questions and Articles on Vitamin D

Can vitamin D-crease pain?
Vitamin D supplementation reduces pain significantly more than placebo, especially among hospitalized patients with chronic pain conditions.
Do I need to supplement Vitamin D if I drink fortified milk?
It depends...
Can vitamin D cure depression?
Many people get depressed during the winter months, when we produce less vitamin D. So, can supplemental vitamin D cure seasonal depression, and maybe other types of depression? No, alas — but it may help.
5 nutrients that could lift your mood
Many foods can temporarily boost your mood simply because they’re delicious. But healthy foods also contain certain nutrients that may have a more direct and lasting effect on your well-being.
How can you increase testosterone naturally?
When it comes to increasing your testosterone, quality sleep, physical activity, and weight management come first. A few supplements can help sustain healthy testosterone levels, but most supplements marketed as testosterone boosters don’t work, though some can make you believe they do by boosting your libido.
When should I take Vitamin D?
Vitamin D can be taken any time. As it is fat soluble, likely best to take it with a meal.

Things to Note

Primary Function:

Also Known As

Cholecalciferol (Vitamin D3), Ergocalciferol (Vitamin D2)

Do Not Confuse With

Calcitriol or 1, 25-Dihydroxyvitamin D (Hormonally active yet not directly supplemented form)

Goes Well With

  • Calcium (for bone health)

  • Vitamin K (for bone health, and vitamin K may attenuate the risk for vitamin D overdosing)

Caution Notice

Toxicity from vitamin D is mediated by altering calcium metabolism, which is potentially lethal. Doses should not exceed 10,000IU daily unless supervised by a medical professional.

  • Vitamin D is usually seen as non-stimulatory

  • Vitamin D may have enhanced absorption when taken with meals

Want the unbiased truth about vitamin D?

We've created a fact sheet that neatly summarizes the scientific research on vitamin D.

Click here to see all 458 references.