Although many symptoms of vitamin D deficiency are mild and go unnoticed, the most common symptoms include muscle weakness or bone pain, according to WebMD. Some people may also feel more fatigued than usual.
Vitamin D deficiencies can occur if exposure to sunlight is limited, because when skin is exposed to sunlight, the body naturally produces vitamin D, according to WebMD. Certain diets may lead to vitamin deficiencies, too. For example, a strict vegan diet with food sources that are not animal-based may not include the necessary levels of vitamin D without consuming supplements with added vitamins each day. Individuals with dark skin pigment are also at risk for vitamin D deficiencies because the pigment melanin restricts and reduces the production of vitamin D when exposed to sunlight.
People who are overweight, obese or pregnant are especially at risk for vitamin D deficiencies and should consume daily supplements to increase the amount of vitamin D absorbed, according to the Vitamin D Council. Older people are also at risk because the skin is thinner and unable to produce as much vitamin D as younger people with thicker skin.
To diagnose a vitamin D deficiency, physicians test the 25(OH)D levels in the blood, explains the Vitamin D Council.