Vitamin D, known as the “sunshine” vitamin, is a fat-soluble (stored in fat tissue) vitamin which is manufactured in the body when ultraviolet light from the sun is absorbed through the skin. Lifestyle and diet choices can deplete vitamin D or help to block the body’s production or absorption of the vitamin leading to a vitamin D deficiency.
The Functions of Vitamin D
Vitamin D plays an important and diverse role in the body. Vitamin D aids the body’s absorption of calcium in the digestive tract, regulates the level of calcium and phosphorous in the blood and aids bone growth and remodeling. Vitamin D also regulates neuromuscular and immune functions and helps reduce inflammation.
Sources of Vitamin D
The primary source of Vitamin D is the sun. Exposure to sunlight from 10 a.m. to 3 p.m. for an average of 15 minutes, 2 times per week on bare skin, can maintain the body’s level of vitamin D. Other natural sources of Vitamin D are fish such as, salmon, tuna and mackerel. Cod liver oil is also a good source of vitamin D. Oysters, beef liver, egg yolks and mushrooms contain Vitamin D as do foods such as milk, cereals and juices which are fortified with Vitamin D.
Vitamin D Deficiency
Vitamin D deficiency is influenced by many factors. Extended periods of cloud cover, smog and extreme pollution can block sunlight, affecting the amount of sunlight absorbed. Also, the limited amount of sunlight available to people living above 42 degrees latitude inhibits the body’s production of an adequate amount of vitamin D. This affects Americans living above a line that extends from the California northern border to Boston, Massachusetts.
The use of sunscreen over SPF 8 blocks UV absorption, which can limit the body’s production of vitamin D, as can the level of melanin in the skin. Vitamin D deficiency may also occur if the kidneys’ ability to convert vitamin D to its active form is inhibited. A lack of absorption in the digestive tract can also limit the body’s access to vitamin D. Lactose intolerance and strict vegetarianism can lead to a vitamin D deficiency. Windows also inhibit vitamin D as they do not allow UVB light to penetrate.
Vitamin D deficiency can lead to many health issues such as rickets, Osteomalacia and Osteoporosis. Asthma, cancer and diabetes have been associated with a vitamin D deficiency. There is also some evidence that a vitamin D deficiency can lead to depression and schizophrenia
People at Risk for Vitamin D Deficiency
Some groups of people seem to be at higher risk for a vitamin D deficiency than others and may need to consider vitamin D supplements. Breast fed infants may be at risk due to the possible lack of vitamin D in breast milk. Keeping infants out of direct sunlight may also lead to a lack of vitamin D. Individuals over the age of 50 may experience decreased ability to absorb UV rays and kidneys may not function properly to convert vitamin D. People with darker skin have greater amounts of melanin which reduces the skin’s ability to absorb sunlight. An exception is African American people who have several protective factors that decrease the risk of vitamin D deficiency.
Overweight or obese individuals are at a higher risk for a vitamin D deficiency because large amounts of body fat inhibit proper absorption and distribution of vitamin D, increasing their risk of vitamin D deficiency. Further, gastric by-pass patients are at risk since the gastric by-pass procedure circumvents the area of the small intestine where vitamin D is absorbed.