Who knew basking in the sun could actually play a role in achieving optimal nutrition? The majority of our nutrient intake occurs through diet, but one vitamin in particular is singularly unique. Vitamin D, one of the fat-soluble vitamins, breaks the rules when it comes to the true definition of a vitamin. Although vitamin D is essential to life, it not only comes from your diet, but it can also be made by the body with a little help from the sun.
The ultraviolet (UV) B rays from the sun can penetrate our exposed skin, which converts a particular compound into previtamin D, which then goes on to make vitamin D. Although there are no published guidelines on sun exposure times required for vitamin D synthesis, some researchers report in as little as 5 to 30 minutes, between the hours of 10 a.m. and 3 p.m., twice weekly may be adequate. However, there are several factors that can decrease our body’s ability to make vitamin D such as clothing, sunscreen, cloud cover, the season, pollution and skin color.
Regardless of the need for sunscreen-free time outdoors in order to make vitamin D, the proposed time is relatively short and does not trump the importance of using sunscreen in order to avoid long-term skin damage and prevent skin cancer.
The less time you spend outdoors and the darker your skin pigmentation is, the more important dietary intake becomes in order to meet vitamin D requirements. For adults age 19 to 70, the Food and Nutrition Board at the Institute of Medicine of the National Academies has set the Recommended Daily Allowance at 600 international units (IU) based on limited sun exposure. Fortified foods such as milk, yogurt, cereal and orange juice provide the majority of our dietary intake of vitamin D. Foods with naturally occurring vitamin D include cod liver oil, salmon, tuna, swordfish, beef liver, eggs and cheese.
- 3 oz. Swordfish565 IU
- 3 oz. Salmon 450 IU
- 3 oz. Tuna, canned 150 IU
- 8 oz. OJ, fortified 140 IU
- 1 Large Eggland’s Best Egg 120 IU
- 8 oz. Skim Milk 100 IU
- 1 Large Egg 40 IU
The recommended intakes for vitamin D were set in order to achieve optimal bone health, which is what vitamin D is best known for. Vitamin D maintains the delicate balance between calcium and phosphorus levels and allows our body to absorb calcium from the foods we eat, and promotes calcium uptake by the bones, which helps to keep them strong. Without adequate vitamin D our bones can become weak and brittle and lead to bone diseases such as rickets and osteoporosis. In addition to bone health, we now know that vitamin D has many other roles in our body including cell growth, immune function and disease prevention, including a potential link to certain cancers.