Did you know that when you’re soaking up the sun, your body is also producing a hefty dose of Vitamin D? When skin is exposed to the ultraviolet B ray emitted by the sun, the cholesterol in skin cells works to start the metabolic processes that are required to synthesize Vitamin D from those rays. Very few foods naturally contain Vitamin D making sunlight an important source of this essential nutrient. In fact, in the 20th century when work shifted from the farm to more industrial, indoor settings the incidence of Vitamin D deficiencies sharply increased. Season, time of day, cloud cover, pollution, skin melanin content, and sunscreen are among the factors that affect UV radiation exposure and vitamin D synthesis. It has been suggested by some vitamin D researchers that approximately 5–30 minutes of sun exposure between 10 AM and 3 PM at least twice a week to the face, arms, legs, or back without sunscreen usually leads to sufficient vitamin D synthesis. It is important to note, however, that UVB rays are a known carcinogen and it is prudent to limit exposure from the sun and/or tanning beds and to apply sunscreen regularly.
This important nutrient has many functions in the body. Strong, healthy bones are typically associated with an adequate intake of calcium, however, without enough Vitamin D, calcium cannot be absorbed making the sunshine vitamin essential to building and maintaining bones. Low levels of vitamin D lead to low bone calcium stores, increasing the risk of fractures. When it was discovered that Vitamin D is necessary for optimal calcium absorption, the United States began to fortify milk, a natural source of calcium, with the nutrient. As a result, the occurrence of rickets, a painful disease that causes softening and bowing of the bones, began to decrease in children. Vitamin D also brings calcium and phosphorus to our teeth to maintain their strength and structure, and helps regulate how much calcium remains in our blood. If blood calcium falls too low, cramping and muscle spasms can occur. It is also involved in the functioning of the muscular, nervous, and immune system while research suggests that vitamin D, especially when taken with calcium, might help prevent certain cancers and long-term vitamin D supplementation reduces the risk of multiple sclerosis.
Only a few foods are natural sources of Vitamin D; fatty fish such as tuna and salmon as well as fish oils are potent sources while beef liver, cheese, and egg yolks contribute small amounts. Additionally, mushrooms that are grown under ultraviolet light contain Vitamin D. Fortified foods in addition to milk include certain cereals, orange juice, yogurt, margarine, and plant based milks like almond or soy milk. Obtaining adequate amounts through diet can be difficult and for certain populations, including those with dark skin, malabsorption issues, breastfed infants, or do not expose their skin to the sun will benefit from a daily Vitamin D supplement.