How Much Vitamin D Do I Need, and Should I Take Supplements?

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 of it. Is taking a supplement really necessary?

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

But Large randomized clinical trials It has been shown over the past few years that vitamin D is not the panacea some people think. Bottom line: The vast majority of Americans already get all the vitamin D they need from their diet and from sunlight.

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

The shift in vitamin D has left many people confused. To understand how this happens, let’s start with the difference between observational studies and randomized trials. Observational studies do exactly what their name suggests: observe what people are doing and analyze data. Randomized trials are experiments that change what people do, similar to flipping a coin determining who gets a vitamin D pill and who gets a placebo, then checking to see who does the best. Previous monitoring work showed an association between vitamin D levels and risk of chronic disease, but this association could not prove causation and may have been due to other factors.

In 2009, my colleagues and I began a study to help fill in the gaps, and search for clearer answers about whether nutritional supplements can prevent heart disease, stroke, and cancer. A nationwide randomized trial, called 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 per day, without knowing which unit they were taking.

The first results, published in 2019, did not find a statistically significant reduction in cardiovascular disease or cancer. Other randomized trials have also found no clear benefits of vitamin D supplementation for these diseases. For example, we published Meta-analysis Considering vitamin D supplementation and cardiovascular disease risk in 21 randomized trials involving more than 83,000 people. This analysis did not find a single trial showing a cardiovascular benefit.

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My colleagues and I have conducted additional studies from VITAL that show that vitamin D supplementation does not reduce the risk of cognitive decline, depression, macular degeneration, atrial fibrillation, or many other health conditions. The latest report showed no decrease in Bone fracture rate Once upon a time the most common vitamin benefit.

In other words, vitamin D is not a cure-all. But it has shown promising results in two main areas.

At VITAL, we found that vitamin D supplementation may have benefits in reducing autoimmune disease and advanced (metastatic or fatal) cancer. Supplementation appears to reduce the risk of autoimmune diseases such as rheumatoid arthritis and psoriasis by approximately 22 percent and advanced cancer 17 percent (Without reducing other cancers). Our team is conducting more research to dig deeper into these findings, as well as to explore whether the effects of vitamin D differ depending on genetic factors.

Other studies have suggested that vitamin D may improve immune function and help calm inflammation, which may help explain this potential link Between vitamin and better results for the Corona virus. Me and my colleagues are moving forward random experiment From 2,024 nationwide participants to see if vitamin D affects the likelihood of developing COVID-19 infection, the risk of severe symptoms and the development of COVID-19 disease. The results are expected to be published later this year.

Meanwhile, as the epidemic continues, it is reasonable (but not necessary) for healthy adults to supplement low to moderate amounts of the vitamin – about 1,000-2,000 IU per day. These amounts have been shown to be safe in the long term. Taking very high doses or “megadoses” (such as taking more than 6000 IU daily) over the long term has not been studied and may increase the risk of high blood calcium levels, kidney stones, and other health problems.

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If you are part of a high-risk group for vitamin D deficiency, talk to your doctor about it Take a supplement and test your vitamin D levels in your blood. This includes those who live in nursing homes, where there may be little exposure to the sun; Those with certain dietary restrictions such as severe lactose intolerance; those with malabsorption conditions such as Crohn’s disease or celiac disease; and those being treated for osteoporosis or other bone health problems.

Otherwise, if you feel fine and healthy, a vitamin D test is likely to be a waste of money. US Preventive Services Task Force Didn’t find enough evidence To recommend routine screening because no study has clearly shown that it is associated with better health outcomes. thresholds Shortage Recommended blood levels vary across organizations, countries and laboratories, which casts further doubt on the usefulness of the test. For example, while a file National Academy of Medicine A level at or above 20 ng/ml is suggested, and 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 some simple steps to increase your intake instead.

The National Academy He recommends 600 IU of vitamin D per day for adults up to age 70 and 800 IU over this age. In the United States, foods such as dairy products, grains, and orange juice are often fortified with vitamin D (countries that do not support foods have higher rates of vitamin D deficiency.) Checking nutrition labels can help you make better decisions about which 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 in the middle of the day is usually enough sunlight for the skin to synthesize vitamin D. This may also be accidental exposure to sunlight, such as while on errands. The best idea for your health is to exercise outdoors, such as playing sports or running. The use of sunscreen reduces the absorption of sunlight but is necessary to prevent skin cancer and premature aging of the skin, if exposure to the sun continues.

Although taking the pill is much easier than being physically active and eating healthy, the latter two will do more to keep you healthy and reduce your risk of cardiovascular disease, cancer, and diabetes. Taking supplements will never be a substitute for a healthy diet and lifestyle.

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