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Vitamin D: More Is Not Always Better

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The past couple of decades have produced a raft of research suggesting that vitamin D has wide-ranging health benefits, and it seems that more people are catching on that they need to keep their stores topped up. Tapping data from the National Health and Nutrition Examination Survey (NHANES), researchers at the University of Minnesota found that among nearly 40,000 adults, the prevalence of daily vitamin D supplementation of 1,000 International Units or more rose from 0.3% in 1999–2000 to 18.2% in 2013–2014, according to a research letter published in the Journal of the American Medical Association.

Somewhat alarmingly, findings also showed that in 2013–2014, the prevalence of supplemental intake of 4,000 IU or more was 3.2%, compared with 0.1% before 2005–2006.

The Institute of Medicine of the National Academies sets the safe daily upper limit for daily vitamin D intake at 4,000 IU. Going consistently higher raises the risk of adverse effects, including blood vessel calcification, which can eventually damage the heart, liver and other organs. With winter gloom upon us, it’s important to be cognizant of getting enough vitamin D through food and supplementation, since deficiencies are still widely reported, but overdosing isn’t the answer. For most people, daily supplementation of 1,000 IU should suffice, but precise amounts should be discussed with a physician.

Matthew Kadey, MS, RD

Matthew Kadey, MS, RD, is a James Beard Award–winning food journalist, dietitian and author of the cookbook Rocket Fuel: Power-Packed Food for Sport + Adventure (VeloPress 2016). He has written for dozens of magazines, including Runner’s World, Men’s Health, Shape, Men’s Fitness and Muscle and Fitness.

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