I know the body makes its own vitamin D when the skin is exposed to sunlight, but I've heard that sunscreens prevent that from happening. Is that true?
Yes, it is true. And experts offer conflicting guidance on the topic, depending on what they believe carries more risk: a vitamin D deficiency or the potential to develop skin cancer.
First, some background. Vitamin D is a fat-soluble vitamin that's found naturally in only a few foods, including fatty fish such as salmon, sardines, and tuna canned in oil. Some foods, including milk and many breakfast cereals, are fortified with vitamin D, which helps the body absorb calcium.
For vitamin D, the recommended amount to get each day increases with age, from 5 micrograms or 200 International Units (IUs) per day up to age 50; to 10 micrograms or 400 IUs per day from 51 to 70 years; to 15 micrograms or 600 IUs per day for people 71 and older. Why? Well, the older you are, the more trouble your body has in synthesizing vitamin D from exposure to sunlight.
This makes older adults at risk for vitamin D deficiency. Other at-risk groups include anyone with limited sun exposure; people with dark skin (the melanin in darker skin reduces the ability to produce vitamin D from sunlight); and people who are obese (fat cells hold onto vitamin D, reducing the amount in the body's circulation system).
The Office of Dietary Supplements with the National Institutes of Health cites studies that suggest between 5 and 30 minutes of sun exposure between 10 a.m. and 3 p.m. at least twice a week to the face, arms, legs, or back without sunscreen usually offers enough sunlight to give you enough vitamin D stores. However, the Skin Cancer Foundation takes issue with that kind of recommendation, citing research that indicates that even a small amount of unprotected exposure to the sun's ultraviolet rays "contributes to cumulative skin damage, accelerating aging and increasing our lifetime risk of skin cancer."
What's the answer? First, try tracking your intake of vitamin D for a few days. The Daily Value for vitamin D on Nutrition Facts labels is 10 micrograms or 400 IUs -- the recommended amount for people 50 or younger. The amount is listed as a percentage, so if you're eating a food with 25 percent of vitamin D, just add up the percentages until you reach 100 percent if you're 50 or younger -- keep counting to 200 percent if you're between 51 and 70, or 300 percent if you're 71 or older. Be sure to count a multivitamin if you take one. If you find you're not consuming enough vitamin D, ask your doctor about additional supplementation, or the relative risks you might face with additional sun exposure.
Chow Line is a service of Ohio State University Extension and the Ohio Agricultural Research and Development Center. Send questions to Chow Line, c/o Martha Filipic, 2021 Coffey Road, Columbus, OH, 43210-1044, or firstname.lastname@example.org.
Editor: This column was reviewed by Lydia Medeiros, nutrition specialist with Ohio State University Extension and the Ohio Agricultural Research and Development Center; and professor of human nutrition in the College of Education and Human Ecology.