In nutritional terms, the word "essential" is used to denote an nutrient that your body is incapable of manufacturing on its own but requires in order to survive and thrive. Cholecalciferol, or vitamin D, is one of the thirteen essential vitamins known to affect human health. If you're deficient in vitamin D, you may experience a number of negative consequences, such as rickets, osteomalacia and muscle pain and weakness. Several different factors can affect your ability to absorb vitamin D.
Breastfeeding
Vitamin D is not adequately represented in human breast milk. As a result of this deficiency, exclusively breast-fed infants are at greater risk of not absorbing enough vitamin D to meet their needs. According to the Linus Pauling Institute, the 25 IUs of vitamin D typically found in a liter of human breast milk falls far short of supplying the needs of a growing infant. The American Academy of Pediatrics advises mothers who breastfeed to supplement their infants' diets with 400 IU of vitamin D daily.
Inadequate Sun Exposure
Vitamin D is unique among vitamins in that your skin can synthesize it, using ultraviolet radiation from the sun. Most of the vitamin D that humans receive is through this method. Any factor that inhibits your ability to absorb sunlight can hinder your vitamin D supply. Dark-skinned people absorb less UV radiation and may be at greater risk for vitamin D deficiency. Lack of access to outdoor activity can reduce sun exposure and sunlight through window glass will not aid in vitamin D synthesis. The use of sunblock is a smart choice for avoiding deadly skin cancers, but does have the unfortunate effect of decreasing vitamin D synthesis. Similar effects result from covering your skin with clothing.
Fat Malabsorption Syndromes
Vitamin D is a fat-soluble vitamin, meaning that it is absorbed via the use of bile acids much like fats. If you have a disorder that affects your body's ability to produce bile acids or otherwise hinders fat absorption, such as Crohn's disease or celiac disease, you are at greater risk of becoming deficient in vitamin D.
Aging
As you grow older, your skin becomes less able to synthesize vitamin D. Elderly people living in institutions may also be limited in their access to direct sun exposure, and may require vitamin D supplementation to fulfill their bodies' needs.
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