A blood test is the only way to measure vitamin D levels accurately, states Healthline. Although vitamin D deficiency usually does not cause noticeable symptoms, some people experience bone pain, muscle and joint pain or weakness, fatigue or tiredness, and depression. Risk factors for vitamin D deficiency include avoiding the sun, obesity, digestive disease and chronic kidney disease. Senior citizens over the age of 65 and people with darker skin tones are also at increased risk.
For optimal heath, people should aim for a vitamin D level of 50 nanograms per milliliter, according to the Vitamin D Council. Treatment for vitamin D deficiency typically involves the use of vitamin D supplements, states Healthline.
The human body produces vitamin D when bare skin receives exposure to direct sunlight, explains the Vitamin D Council. The exact amount of vitamin D a person gets from sun exposure depends on location, time of day, the color of the person's skin and the amount of skin exposed to the sun. Food sources of vitamin D include fortified milk, egg yolks and beef liver.
Vitamin D helps the body utilize calcium and is necessary for healthy, strong bones, states WebMD. As of 2015, research indicates that vitamin D may play a role in protecting against hypertension, diabetes and glucose intolerance.