Vitamin D, a fat-soluble vitamin, helps your body regulate calcium and phosphate levels. You obtain vitamin D via sun exposure and diet, but these forms of the vitamins are biologically inert; processes in your liver and kidneys convert these inactive forms to structures that your body can use. As its main function, vitamin D facilitates calcium absorption in your small intestine; consequently, vitamin D deficiency primarily affects calcium levels.
Vitamin D naturally occurs in very small quantities in very few foods. The vitamin D in most of the food you eat is added through nutrient fortification. As a result, groups at risk for vitamin D deficiency include people who do not have access to fortified foods or who do not get adequate sun exposure. These groups include infants who are exclusively breastfed; the elderly, whose skin cannot synthesize vitamin D as efficiently; and people with fat malabsorption, since vitamin D relies on fat in the small intestine for sufficient absorption.
Prolonged vitamin D deficiency in children results in rickets. Decreased vitamin D in the body inhibits calcium absorption. As a result, the body begins to pull calcium and phosphate from the bones to maintain blood levels, leading to weak and soft bones. Symptoms include bone pain, delayed teeth formation and other dental deformities, impaired growth, short stature, bowlegs and pelvic and spine deformities.
Osteomalacia is the softening of bones in adults caused by a lack of vitamin D. This condition differs from the more familiar osteoporosis, which involves bone demineralization and loss of bone tissue due to a lack of calcium, but they have similar symptoms. Unlike in children with rickets, the bones in adults with osteomalacia have sufficient structure and length, but the decrease in calcium absorption inhibits the construction of new bone to strengthen the existing skeleton. Adults with osteomalacia may experience muscle weakness, fractures from minor injuries and bone pain, especially in the hips.
Seasonal Affective Disorder and Depression
Seasonal affective disorder is a form of depression that occurs typically in the late fall and winter as the number of daylight hours decrease. Reported symptoms include fatigue and moodiness. Some studies have tried to connect low vitamin D levels to seasonal affective disorder and depression. However, more recent studies have shown that vitamin D supplementation does not prevent these disorders, according to the Vitamin D Council. Instead, reports show that vitamin D supplementation in people with depression -- in addition to standard treatment -- may improve outcomes and quality of life.
Vitamin D deficiency by itself does not cause osteoporosis but when combined with long-term calcium deficiency, low levels of vitamin D can accelerate this condition. The U.S. Office of Dietary Supplements notes that several studies associate vitamin D deficiency with a higher risk for prostate, colon and breast cancers. Mounting research also connects vitamin D deficiency with the development of Type 1 and Type 2 diabetes, hypertension and multiple sclerosis.
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