Advice |  Ask a Doctor: How Much Vitamin D Do I Need?  Should I take a supplement?

Advice | Ask a Doctor: How Much Vitamin D Do I Need? Should I take a supplement?

JoAnn E. Manson is chief of preventive medicine at Brigham and Women’s Hospital and professor of medicine at Harvard Medical School.

Q: I keep hearing about the benefits of vitamin D and worry that I’m not getting enough. Is it really necessary to take a supplement?

A: For years people have thought of vitamin D as a miracle supplement that could reduce the risk of developing cancer, cardiovascular disease, diabetes, bone fractures and a long list of other chronic diseases.

But large randomized clinical trials over the past few years have shown that vitamin D is not the panacea some thought it was. Bottom line: the vast majority of Americans already get all the vitamin D they need from their diet and from the sun.

Is it necessary for you to spend money on the supplement? For most healthy adults, the answer is no. We only need low to moderate amounts of the vitamin, and more is not necessarily better.

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The switch to vitamin D has left many people confused. To understand how this happened, let’s start with the difference between observational studies and randomized trials. Observational studies do exactly what their name suggests: observe what people do and analyze the data. Randomized trials are experiments that change what people do, like flipping a coin to decide who gets vitamin D pills and who gets a placebo, and then checking who does better. Previous observational work had shown a link between vitamin D levels and the risk of chronic disease, but this correlation could not prove causation and may be due to other factors.

In 2009, my colleagues and I started a study to help fill the gaps, looking for clearer answers about whether supplementation can prevent heart disease, stroke, and cancer. The national randomized trial, called the VITAL Study, recruited nearly 26,000 adults and followed them for five years. Participants agreed to receive either a placebo or 2,000 international units (IU) of vitamin D daily, without knowing which one they were taking.

The first results, published in 2019, found no statistically significant reduction in cardiovascular disease or cancer. Other randomized trials have also found no clear benefit of vitamin D supplements for these diseases. For example, we published a meta-analysis looking at vitamin D supplements and cardiovascular risk in 21 randomized trials involving over 83,000 people. This review found no trials showing cardiovascular benefit.

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My colleagues and I have conducted other VITAL studies showing that vitamin D supplements do not decrease the risk of cognitive decline, depression, macular degeneration, atrial fibrillation, or several other health conditions. The most recent report showed no reduction in the rate of bone fractures – once the vitamin’s most often touted benefit.

In other words, vitamin D is not a panacea. But it showed promise in two key areas.

In VITAL, we found that vitamin D supplements may have benefits in reducing autoimmune diseases and advanced (metastatic or fatal) cancer. Supplementation appears to reduce the risk of developing autoimmune diseases such as rheumatoid arthritis and psoriasis by around 22% and advanced cancer by 17% (without decreasing other cancers). Our team is continuing their research to explore these findings further, as well as to determine whether the effects of vitamin D vary based on genetic factors.

Other studies have indicated that vitamin D may improve immune function and help reduce inflammation, which may help explain the possible link between the vitamin and better covid outcomes. My colleagues and I are conducting a nationwide randomized trial of 2,024 participants to determine whether vitamin D affects the likelihood of covid-19 infection, the risk of severe symptoms, and the development of long covid. The results are expected to be released later this year.

In the meantime, as the pandemic drags on, it’s reasonable (but not essential) for healthy adults to supplement with low to moderate amounts of the vitamin — around 1,000 to 2,000 IU per day. These amounts have been shown to be safe in the long term. Taking very high doses, or “mega-dosing” (such as taking more than 6,000 IU per day), has not been studied long term and may increase the risk of high blood calcium levels. kidney stones and other health problems.

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If you are in a high risk group for vitamin D deficiency, talk to your doctor taking a supplement and having vitamin D blood levels tested. This includes those who live in nursing homes, where there may be little exposure to sunlight; those with certain dietary restrictions such as severe lactose intolerance; those with malabsorptive conditions such as Crohn’s disease or celiac disease; and those being treated for osteoporosis or other bone health issues.

Otherwise, if you feel fine and are healthy, the vitamin D test is probably a waste of money. The US Preventive Services Task Force did not find enough evidence to recommend routine screening, as no studies have clearly shown it is linked to better health outcomes. Deficiency thresholds and recommended blood levels vary between organizations, countries and laboratories, casting further doubt on the usefulness of the test. For example, while the National Academy of Medicine suggests a level of 20 ng/ml or higher, some organizations recommend higher levels.

If you’re still concerned about your vitamin D levels but aren’t in a high-risk group, try taking a few simple steps to increase your intake instead.

The National Academy recommends 600 IU of vitamin D daily for adults up to age 70 and 800 IU beyond that age. In the United States, foods such as dairy, cereal, and orange juice are often fortified with vitamin D. (Countries that do not fortify foods have higher rates of vitamin D deficiency.) Checking nutrition labels can help you make better decisions about what foods to buy. Wild mushrooms and fatty fish, such as salmon, sardines and tuna, are other sources.

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Also, going out for a 15-minute walk a few times a week at noon is usually enough for the skin to synthesize vitamin D. It can even be accidental sun exposure, such as while running errands. An even better idea for your health would be to exercise outside, such as playing sports or jogging. Wearing sunscreen decreases sun absorption, but is crucial in preventing skin cancer and premature skin aging, if sun exposure is prolonged.

While popping a pill is much easier than being physically active outdoors and eating healthy, the latter two will do more to keep you healthy and reduce your risk of cardiovascular disease, cancer, and heart disease. diabetes. Taking a supplement will never replace a healthy diet and lifestyle.

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