Perhaps you’re getting enough sleep, and yet you seem unusually fatigued during much of the day. Even taking a nap doesn’t help. The cause of the problem may be a lack of vitamin D. Fatigue is a well-identified symptom for those who run low on this essential nutrient of the human body.


Vitamin D deficiency often begins to show up in people as summer ends, the days get shorter, and people stay inside more during the winter months. That’s because exposure to sunlight is necessary for the body to manufacture its own vitamin D. When the UVB rays of the sun strike cholesterol in the skin, the result is a biochemical reaction that generates vitamin D.


The body needs at least 15 to 30 minutes of direct exposure to sunlight about three days per week to maintain internal vitamin D production.


Low vitamin D can produce other problems, including muscle weakness, depression, and seemingly unexplainable aches and pains. Those are just initial outward symptoms, however. 


A consistent lack of vitamin D can lead to other major conditions, such as heart disease, diabetes, and high blood pressure. Several forms of cancer have been associated with low vitamin D, including prostate, colon, and breast cancer. 


Finally, vitamin D is crucial to the maintenance of healthy bones. A well-known disease caused by vitamin D deficiency is rickets, a painful condition that deforms the skeletal frame. The body needs vitamin D to drive a reaction between phosphorus and calcium to produce strong, healthy bones.


In addition to getting enough sun, several foods have been identified as excellent sources of vitamin D. In the top tier is fish, especially cod liver oil. Just one teaspoon holds 1,360 IU (International Units) of vitamin D. Three ounces of swordfish has 566 IU, three ounces of sockeye salmon has 447 IU, and three ounces of canned tuna has 154.


Milk and orange juice that has been fortified with vitamin D are excellent ways to get your daily allowance in drinks that are part of a healthy diet.


Finally, as people age, they need to take in more vitamin D. The recommended daily allowance for infants is 400 IUs per day, while those who reach age 70 will require 800 IUs of vitamin D per day.