Vitamin D is a fat soluble vitamin, found in some foods that is needed for health and to maintain strong bones. It does so by helping the body absorb calcium (one of bone’s main building blocks) from food and supplements. Most vitamin D – 80% to 90% of what the body gets – is obtained through exposure to sunlight.
People who get too little vitamin D may develop soft, thin, and brittle bones, a condition known as rickets in children and osteomalacia in adults. Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and to prevent. Without sufficient vitamin D, bones can become thin, brittle, or misshapen.
Vitamin D is important to the body in many other ways as well. Muscles need it to move, for example, nerves need it to carry messages between the brain and every body part, and the immune system needs vitamin D to fight off invading bacteria and viruses. Vitamin D is found in cells throughout the body.
Vitamin D deficiency
Deficiencies of vitamin D are common, especially in industrialized countries in northern latitudes, where sun exposure is typically infrequent. Low levels of vitamin D may be indicated by porous bones, weak muscles and easy fracturing.
People with milk allergy, lactose intolerance, ovo-vegetarians and vegans are at risk to have lower vitamin D intake. Also, people can become deficient in vitamin D because they don’t consume enough or absorb enough from food, their exposure to sunlight is limited, or their kidneys cannot convert vitamin D to its active form in the body.
Sources of Vitamin D
Very few foods in nature contain vitamin D. The flesh of fatty fish (such as salmon, tuna, and mackerel) and fish liver oils are among the best sources. Small amounts of vitamin D are found in beef liver, cheese, and egg yolks. Some mushrooms provide vitamin D2 in variable amounts. Fortified foods is available now, like milk, cereals, yogurt and other food products. Good food sources are: oily fish (salmon, tuna, swordfish), eggs, liver and beef.
Most people meet their vitamin D needs through exposure to sunlight. People that live far north get it from exposure to sun during the spring, summer, and fall months and store it in the liver and fat. UVB radiation does not penetrate glass, so exposure to sunshine indoors through a window does not produce vitamin D. Sunscreens with a sun protection factor (SPF) of 8 or more appear to block vitamin D-producing UV rays, but in practice people do not apply sufficient amounts, cover all sun-exposed skin, or reapply sunscreen regularly. Therefore, skin likely synthesizes some vitamin D even when it is protected by sunscreen as typically applied.
Vitamin D is found in supplements (and fortified foods) in two different forms: D2 (ergocalciferol) and D3 (cholecalciferol). Both increase vitamin D in the blood. Take your vitamin D3 supplement after your meal. As a fat soluble vitamin it’s better absorbed when taken on full stomach.
Can vitamin D be harmful?
Yes, when amounts in the blood become too high. Symptoms are nausea, vomiting, poor appetite, constipation, weakness, and weight loss. More seriously, it can also raise blood levels of calcium and cause confusion, disorientation, and problems with heart rhythm. Excess vitamin D can also damage the kidneys.
Vitamin D toxicity almost always occurs from overuse of supplements. Excessive sun exposure doesn’t cause vitamin D poisoning because the body limits the amount of this vitamin it produces. The upper limit for vitamin D is 1,000 to 1,500 IU/day for infants, 2,500 to 3,000 IU/day for children 1-8 years, and 4,000 IU/day for children 9 years and older, adults, and pregnant and lactating teens and women.