Nutrition Spotlight | Question: To D or not to D?

With final exams finished and end-of-semester papers handed in, you can finally relax and enjoy that much-anticipated light at the end of the tunnel - sunlight, that is. Although we've been told for decades to protect our skin and eyes from too much sun exposure, as harmful UV rays can lead to skin cancer, wrinkles and cataracts, our skin actually needs some sun exposure. Our bodies utilize UV rays to synthesize vitamin D - an essential nutrient that plays a vital role in our overall health, particularly in bone health. Recently, researchers found that many more people are vitamin D-deficient than previously thought, and this discovery has spawned much debate about too little versus too much sun, and how best to get enough vitamin D. Vitamin D is a fat-soluble vitamin (meaning it is transported and absorbed by your body via fat) that helps build and maintain strong bones by promoting calcium absorption and bone mineralization. The best food sources of vitamin D are fish, eggs, cod liver oil and fortified milk. Two cups (16 fluid ounces) of fortified milk will provide you with the minimum recommended amount of vitamin D per day. It's important to note that not all dairy products (for example, yogurt and cheese) are fortified with vitamin D, so read labels carefully. However, unlike many other vitamins, dietary intake is not the only source of vitamin D. As previously mentioned, our bodies can actually produce vitamin D - given that we get sufficient sun exposure. UV rays from the sun activate a compound in the skin, transforming it into "previtamin D." Previtamin D is then absorbed into the bloodstream, where it travels to the liver and kidneys to be converted to an active form of vitamin D that the body can use. Factors that affect our ability to get adequate UV ray exposure include season, geographic latitude, time of day, cloud cover, smog, skin pigmentation and sunscreen. For example, in the greater Boston area, we don't get enough sunlight exposure from November through February for our bodies to make sufficient vitamin D. So, now that long, hot summer days are quickly approaching, do we pull out the sunscreen, hats and sunglasses to protect our skin from the sun, or do we stretch out on the beach to maximize our sun exposure - and thus, our vitamin D production? According to the American Academy of Dermatology (AAD), everybody, regardless of skin type, should use a sunscreen with a Sun Protection Factor (SPF) of at least 15 year-round, especially on days you plan to be in the sun for more than 20 minutes. Protecting your skin from the sun is crucial, the AAD says, because sun exposure is the most preventable risk factor for skin cancer. But vitamin D is now gaining increased attention for its potential role in actually preventing certain cancers. Dr. Cedric Garland, professor of Family and Preventive Medicine at the University of California - San Diego School Of Medicine, presented data at the American Association for Cancer Research (AACR) meeting just last month suggesting that women with higher vitamin D levels have a significantly reduced risk of breast cancer. Other researchers have linked low vitamin D levels with other types of cancers and even multiple sclerosis. Sunscreens with an SPF of eight or higher block the UV rays that allow the skin to synthesize vitamin D. Thus, protecting your skin while still getting enough sun exposure to make adequate amounts of vitamin D continues to be a topic of debate. Some experts believe that the recommended intake of vitamin D should be increased, some suggest fortifying more foods with vitamin D, and others recommend taking vitamin D supplements. At this point, though, it is agreed that more extensive vitamin D research is necessary before making any of these changes. You'll likely get enough sun exposure this summer doing your everyday activities, so there's no need to bake in the sun all day just to make enough vitamin D. Too much sun can definitely be harmful. As we like to say in the nutrition field, "everything in moderation" - and the case of sun exposure and vitamin D is no exception.Katherine Kwon is a graduate student and dietetic intern at the Friedman School of Nutrition Science and Policy and the Frances Stern Nutrition Center. She has a BS in dietetics from the University of California.