Research on the varied roles of vitamin D is continuing at a rapid clip. We already know that vitamin D is essential for bone health…and now we’re learning more about the ways it contributes to overall good health as well as the perils we face when we don’t get enough of the vitamin.

Bottom Line Personal asked nutrition researcher Ouliana Ziouzenkova, PhD, to parse through the findings of recent studies from around the world supporting the role of vitamin D for our health. Most of the studies used daily supplements of 2,000 international units (IU). This is higher than the recommended dietary allowance (RDA) of 600 IU for adults up to age 70 and 800 IU for adults over age 70 but still in line with what experts recommend for optimal health.

Caution: Before starting to take supplements, talk with your doctor and a nutritionist about the appropriate dosage for you, especially if you have kidney disease or atherosclerosis. Your endocrine and mineral status, bone density, dietary habits and age all should be taken into account.


Vitamin D lowers risk for autoimmune diseases. This Harvard study looked at the potential for vitamin D supplements, taken on their own as well as with omega-3 fatty acids, to prevent autoimmune diseases such as rheumatoid arthritis (RA), polymyalgia rheumatica, autoimmune thyroid disease and psoriasis in middle-aged and older people. Finding: Participants who took 2,000 IU of vitamin D-3 (cholecalciferol) every day for five years, with or without a daily supplement of 1,000 mg of marine-derived omega-3s, reduced their risk for autoimmune diseases by 22% compared with participants who received only placebos. The reduction was the highest for RA at 40%. Because the preventive effects of vitamin D increase over time, the researchers are continuing to follow participants for two more years to see whether the benefits will continue to go up.


Vitamin D reduces risk for type 2 diabetes complications. The deadly complications of type 2 diabetes, notably heart disease, often stem from inflammation in blood vessels. Blood cells known as platelets stick to inflamed blood vessels and form clots. This can have a snowball effect that ultimately could lead to heart attack, stroke, amputation and/or loss of kidney function. To investigate the health effects of vitamin D on people with diabetes, researchers from the National Institute of Pharmaceutical Education and Research in Guwahati, India, gave study participants 60,000 IU of vitamin D-3 per week for three months followed by 60,000 IU per month (2,000 IU daily) for three months as maintenance. Finding: Having a sufficient circulating level of vitamin D reduced platelet activity and oxidative stress. In particular, the serum levels of the well-known inflammatory proteins IL-18 and TNF-alpha were lower—a key factor in reducing or preventing many type 2 diabetes complications.


Vitamin D helps women avoid clots after stroke. Having a vitamin D deficiency is more common in middle-aged and older women than men because of diet, less sun exposure, estrogen loss and other factors. Separately, women have a higher risk than men of developing serious blood clots in a deep artery, most often in a leg, a condition called deep vein thrombosis (DVT). This study, led by researchers at ­China’s Wenzhou Medical University, looked for a connection. Finding: Having vitamin D levels higher than 75 nmol/L (which many experts consider an optimal level as opposed to a “sufficient” level of 50 nmol/L) is linked with lower risk for DVT, and supplementing with vitamin D could help make up for the gender difference in DVT risk.


Vitamin D deficiency hurts heart and circulatory health. Researchers from the South Australian Health and Medical Research Institute in Adelaide found that people with vitamin D deficiency are more likely to suffer from heart disease and high blood pressure than people whose levels of vitamin D were above deficiency. Finding: Participants with the lowest concentrations of vitamin D had double the risk for heart disease than those with sufficient concentrations. Just increasing vitamin D ­levels in the blood to 50 nmol/L offered effective protection from heart disease. (Higher levels of vitamin D didn’t seem to offer further protection for this health threat). The study also found a positive association between adequate vitamin D levels and systolic and diastolic blood pressure levels.

Vitamin D helps protect athletes from the perils of overexertion. Exercise is essential to maintain health and counteract inflammatory processes, but too much exercise can increase inflammation, decrease immune function and expose you to a higher risk for diseases. This is especially true in the face of vitamin D deficiency, which accompanies calcium loss during the stress and excitement of athletic training and competitions, according to researchers in the Department of Movement, Human and Health Sciences at University of Rome in Italy. Some athletes who become vitamin D deficient experience higher levels of oxidative stress and inflammation as well as respiratory infections, fractures and muscle injuries. Finding: Having enough vitamin D counteracts inflammation and balances calcium metabolism. This, in turn, enhances the body’s immune defense and improves the health of muscles, bones and the bone marrow blood cells that work in concert to improve healing, prevent fractures and maintain endocrine health.


There’s more evidence that vitamin D helps you fight off infections. This was a lab-based study conducted by researchers from University of Eastern Finland in Kuopio. It took a close look at vitamin D’s role in fighting off threats to the immune system. Finding: While vitamin D is used as co-therapy for certain conditions, such as psoriasis, for the best immune defense it’s important to be proactive and get your vitamin D level optimized before you get sick, particularly in winter or whenever your exposure to sunlight is scant.


Vitamin D-3, not vitamin D-2, may be the supplement of choice. Researchers at University of Surrey, University of Brighton and Newcastle University, all in the UK, compared the effects of the two readily available forms of vitamin D supplements—vitamin D-2 (ergocalciferol), found in plant foods such as mushrooms, and D-3 (cholecalciferol), found in animal-based foods. Participants took daily supplements of 15 micrograms (600 IU) of either vitamin D-2 or D-3 over a 12-week period in winter. The researchers then used blood samples to examine the difference in the regulation of genes implicated in the immune response. Finding: Vitamin D-3, but not D-2, helped prepare genes for a more robust immune defense. In other words, supplementing with vitamin D-3 was better at enhancing the body’s immune response against bacterial and viral diseases.

The Future of Vitamin D Research

These insights into the health benefits of vitamin D raise new questions about the vitamin’s importance in special population groups, such as how much vitamin D do vegetarians and vegans and people who fast need. Also…

With advances in genetic ­testing, we’re now finding that there are mutations in the genes responsible for converting vitamin D to its ­hormonally active form. Research is needed to find out what levels of the vitamin are needed by people with such mutations.

Blood levels of vitamin D are used to diagnose an overall deficiency, but deficiencies can develop autonomously within the bones, immune cells, kidneys and other organs and lead to diseases. Tissue-specific diagnostics of vitamin deficiencies is key to identifying more preventive strategies in the future.

Valid clinical studies comparing the effects of vitamin D produced with different levels of sun exposure to the dietary and supplemental forms of vitamin D also would be beneficial. This would ensure vitamin D sufficiency based on where you live, the local diet that you follow and the pollutants you might be exposed to.

Best Ways to Get Your Vitamin D

Morning sun, especially when combined with fresh air and exercise.

Diet—in particular, shitake mushrooms, fatty fish, eggs, yogurt with live cultures.

Supplements—the recommended dietary allowance is 600 IU daily up to age 70…800 IU over age 70. Check with your doctor for the appropriate dosage.

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