In the past 20 years, there’s been increased focus on vitamin D, highlighting its potential for benefits beyond bone health, says Howard Sesso, SCD, an associate professor of epidemiology at the Harvard T.H. Chan School of Public Health, thanks to research linking low D levels to a wide range of ailments including arthritis, cancer, diabetes, heart disease, depression, multiple sclerosis, and Parkinson’s disease. However, researchers (including Sesso, who is a leading vitamin D researcher at Brigham and Women’s Hospital in Boston) agree that these findings aren’t yet conclusive, so as with most things involving your health, start by talking with your doctor.
See also Vitamin D: Don't Block It Out
If you decide to take a vitamin D supplement, you may be able to adjust your daily dose (or skip it entirely) during summer when vitamin D–producing sunshine is plentiful. Many experts agree you need 50 percent of your body exposed without sunscreen for 10–20 minutes every day in order to hit your daily vitamin D target.
But be aware: There are many variables that can affect the amount of sun that reaches your skin. For example, the sun’s rays are blocked by the atmosphere during winter months in cities north of the 37th parallel, which extends roughly from San Francisco to Richmond, Virginia. The color of your skin also matters—lighter skin tones synthesize D more efficiently than darker tones. The time of day during which you get sun exposure is also a factor, as is your age. For instance, people older than 70 synthesize much less vitamin D than their younger counterparts.
Checking your D levels requires a simple blood test, says holistic pharmacist Sherry Torkos, and if you’re older than 50 or suffer from achy bones, muscle weakness, or mood swings, there’s a good chance that you, like 1 billion other people worldwide, aren’t getting enough. Although the National Institutes of Health recommends 600 international units (IU) a day for people younger than 70, and 800 IU for those older than 70, some doctors who practice integrative medicine will prescribe upwards of 10,000 IU per day. Meanwhile, the tolerable upper intake level set by the Food and Nutrition Board is 4,000 IU a day for adults and children older than 9.