Vitamin D is a fat-soluble vitamin, which means that it is best absorbed when you eat fat along with it, and it is also stored in your body unlike water soluble nutrients. Vitamin D is used by the body for normal bone development and maintenance by increasing the absorption of calcium, magnesium, and phosphate. In 2011 the prevalence of vitamin D deficiency in America was 41.6%, with the highest rate seen in blacks (82.1%), followed by Hispanics (69.2%). Vitamin D deficiency can lead to rickets in children and osteoporosis in adults. Common symptoms of a deficiency include getting sick or infections often, feeling tired, depression, bone loss, and others. If you feel that you may have a vitamin D deficiency, please talk with your doctor.
Natural Absorption and Deterrents
The most common way American’s obtain their vitamin D is by the sun.It starts when the skin absorbs rays in the invisible ultraviolet B (UVB) part of the light spectrum. The liver and the kidneys also participate to make a form of the vitamin that the body can use. Unfortunately, there are numerous factors that can affect our ability to absorb vitamin D from the sun, which include where you live, your use of sunscreen, skin pigmentation, weight, and age. The farther away you live from the equator the less vitamin D producing UVB light reaches the earths surface during the winter, and typically residents are more bundled up during the winter months which also decrease our UVB exposure. Sunscreen can also decrease your uptake of UVB light, but studies have shown that few people put on enough to block all UVB light from the sun. Melanin is the substance in skin that makes it darker in color. It “competes” for UVB with the substance in the skin that kick-starts the body’s vitamin D production. Unfortunately, as a result, individuals with darker skin tend to require more UVB exposure than light-skinned people in order to generate the same amount of vitamin D. Some studies have shown that being overweight may affect the bioavailability of vitamin D. As we get older, we have lower levels of the substance in the skin that UVB light converts into the vitamin D precursor, and experimental evidence has shown that older people are less efficient at producing vitamin D than younger people.
Food Sources
Vitamin D is found naturally in fatty fish such as mackerel and salmon, mushrooms, egg yolks and liver making it hard to obtain adequate amounts from your diet. Most of the dietary intake of vitamin D among Americans comes from fortified milk products and other fortified foods such as breakfast cereals and orange juice.
Winters Are Long
Here in Wyoming our winter months can make it harder to get adequate UVB light for vitamin D synthesis in the body, because we are farther away from the equator and typically in the winter, we bundle up more and spend less time outdoors. If this is the case for you, you may want to talk with your doctor to see if a seasonal vitamin D supplement would benefit you. So, how much vitamin D do you need? Adults 19-70 years old need 600 international units (IU) per day, and adults 71 years and older need 800 IU. You can also help boost your vitamin D intake during the winter months by increasing your intake of naturally occurring and fortified vitamin D foods. See below for a tasty entrée loaded with vitamin D, serve it with a glass of low-fat milk, and your body will thank you!
Written by University of Wyoming Extension Nutrition and Food Safety Educator Shelley Balls, MDA, RD, LD
Sources:
- Forrest K, Stuhldreher W. Prevalence and correlates of vitamin D deficiency in US adults. Nutrition Research. 2011;31(1):48-54. doi:10.1016/j.nutres.2010.12.001
- Parva N, Tadepalli S, Singh P et al. Prevalence of Vitamin D Deficiency and Associated Risk Factors in the US Population (2011-2012). Cureus. 2018;10(6). doi:10.7759/cureus.2741
- National Institutes of Health, NIH