Found in virtually every tissue and cell in the body and enabling many biological functions, vitamin D comes from three sources: food, supplements and the sun. It's also one of four fat-soluble vitamins, the other three being vitamins A, E and K. Vitamin D has two forms that are relevant to human health: vitamin D2 (produced by some plants) and vitamin D3 (synthesized when skin is exposed to ultraviolet rays). Its primary role is in the regulation and absorption of calcium and phosphorus. Rickets in children and osteomalacia, osteopenia and osteoporosis in adults are the most well-established consequences of vitamin D deficiency. In addition, hundreds of studies over the past 15 years underscore interest in vitamin D's potential role in risk reduction of other diseases, including some cancers, heart disease, stroke, diabetes, autoimmune diseases, infectious diseases, neurocognitive disorders and mortality. While much of this research is ongoing and may provide more definitive answers in the future, the current general consensus is that — with the exception of bone health — the relationship between vitamin D and other health conditions is still unclear.
However, there is little consensus as to what constitutes vitamin D deficiency and optimal intake. Vitamin D status is assessed through a simple blood test and measured as nanograms of 25-hydroxy vitamin D per milliliter of blood, or ng/ml. Depending on who you ask, sufficient levels range between 20-50 ng/ml and 40-80 ng/ml, while recommended intakes for adults are as low as 600 IU per day and as high as 5,000 IU per day. Where experts do agree is that most American adults fall short in the vitamin D department. At particular risk are overweight or obese individuals or those who have undergone gastric bypass surgery, older adults, people with limited sun exposure and people with inflammatory bowel disease or other conditions causing fat malabsorption. Identified as “an underconsumed nutrient” in the 2015-2020 Dietary Guidelines for Americans, achieving adequate vitamin D intake from food alone may be challenging. There is a relatively limited number of foods rich in vitamin D — the best sources being fatty fish such as salmon, sardines, trout, mackerel and tuna, in addition to fish liver oils.
In fact, most dietary vitamin D comes from fortified foods such as milks, juices and breakfast cereals. While some sources advocate sensible sun exposure for vitamin D production, exposure without sunscreen to block UV rays poses an increased risk of skin cancer — although this potentially could change pending the release of vitamin D-friendly sunscreen products. In the meantime, supplemental vitamin D may be necessary to fill nutrient gaps. Vitamin D3, which is made in part from sheep's wool, is the preferred form because it is more efficiently converted in the liver to the form the body uses than vitamin D2 (which is commonly found in medical prescriptions but is harder to measure in blood). When counseling vegan clients, however, RDNs should recommend vitamin D2 supplements. Supplements can be taken daily, weekly or monthly, and many health-care providers recommend starting with a higher dose, then reducing after a month or two and continuing with a maintenance dose. Multivitamins also may provide some vitamin D — typically 400 IU, but with a range between 200 IUs and 10,000 IUs.
Whereas safety concerns often abound with high levels of fat-soluble vitamins, vitamin D appears to be the exception. Vitamin D toxicity, one of the rarest medical conditions, is typically due to extremely high doses of 50,000 IU daily but can occur at as low as 10,000 IU per day. The tolerable upper intake level is 4,000 IU for adults. “Too much vitamin D can increase calcium levels, which can lead to calcification of kidneys and blood vessels, high blood levels of calcium and phosphorus usually occurring when serum levels reach 200-250 ng/ml,” says Michael Holick, PhD, MD. “When toxic levels are reached, consequences disappear once the supplement is discontinued unless the toxicity has persisted for long periods of time.” Kathleen Zelman, MPH, RD, is the director of nutrition at WebMD.Vitamin D is an essential vitamin required by the body for the absorption of calcium, bone development, immune functioning, and alleviation of inflammation. Vitamin D deficiency can lead to rickets, a weakened immune system, increased cancer risk, poor hair growth, and osteomalacia.
Excess vitamin D can cause the body to absorb too much calcium, leading to increased risk of heart disease and kidney stones. The current U.S. Daily Value for vitamin D is 600 IU (international units) and the toxicity threshold is thought to be 10,000 to 40,000 IU/day.2 Sometimes vitamin D values are given in micrograms (mcg,μg), when this is the case remember that 1μg=40IU for Vitamin D. Vitamin D is oil soluble, which means you need to eat fat to absorb it. Natural foods high in vitamin D include fish oils, fatty fish, mushrooms, beef liver, cheese, and egg yolks. Vitamin D is also naturally made by your body when you expose your skin to the sun and is called the sunshine vitamin. In addition, vitamin D is widely added to many foods such as milk and orange juice, and can also simply be consumed as a supplement. Below is a list of high vitamin D foods, for more see the list of foods rich in vitamin D2 (Ergocalciferol) and foods rich in vitamin D3 (Cholecalciferol). Maitake (131%), Morel (23%), Chanterelle (19%), Oyster (4%) and White (1%).
Smoked Salmon (97%), Swordfish (94%), Canned Trout (86%), Salmon (75%), Smoked White Fish (73%), Mackerel (65%), Canned Mackerel (43%), Tuna Canned in Oil (38%), Halibut (33%), Herring (30%), Sardine (27%), Rockfish (26%), Tilapia (21%), Sole & Flounder (20%), and Tuna Steak (12%). Total Raisin Bran (17%), Kellogg's Raisin Bran (15%), Kellogg's All Bran (9%), Cheerios, Kellogg's All-Bran Complete Wheat Flakes & Special K (7%). Lite Silken Tofu (21%), Sprouted Tofu, Extra Firm Tofu & Firm Tofu (14%), and Soy Yogurt (3%). Buttermilk, Fortified Low Fat Fruit Yogurt, Fortified Whole Milk, Fortified Goat's Milk (21%), Fortified Semi-Skim Milk (20%), Fortified Skim Milk (19%). Spare Ribs (15%), Turkey & Pork Sausage (12%), Pork Shoulder (9%), and Pork Loin (8%). Raw, Scrambled, Poached and Omelet (7%), Duck Egg (8%), and Goose Egg (16%). Soymilk (20%), Almond Milk, Chocolate Almond Milk, Nonsoy Imitation Milk, Rice Drink (17%). Health Benefits of Vitamin D
Osteoporosis Protection - Vitamin D is necessary for the proper absorption of Calcium which strengthens bones and helps to prevent osteoporosis. Vitamin D mainly benefits older adults, people who have difficulty exercising, postmenopausal women, and individuals on long term steroid therapy.3,4 Decreased Cancer Risk - Vitamin D has been shown to reduce cancer risk, particularly for colon cancer.5-7 People at Risk of a Vitamin D Deficiency Breastfed Infants Who are Not in the Sun - The amount of vitamin D in breast milk depends on the amount of vitamin D in the mother. However, breast-milk typically does not contain adequate amounts of vitamin D. Be sure infants get at least some exposure to the sun (at least 10-20 minutes) to ensure adequate levels of vitamin D.8 Older Adults - As skin ages it is less and less able to make vitamin D from the sun, so vitamin D has to be attained from People With Little Sun Exposure on the Skin - Wearing sunscreen, or lots of clothing, hampers the creation of vitamin D from the sun.9,10
People with Darker Skin - Melanin, a pigment found in skin, reduces the body's ability to manufacture vitamin D from the sun.5 People who have Problems Absorbing Fat, or are on Extreme Low Fat Diets - Vitamin D is fat soluble, which means it is found in fats, and your body has to be able to digest fats in order for you to absorb the vitamin D.11 People Who are Obese, or People Who have Had Gastric Bypass Surgery - Excess fat in the body absorbs vitamin D, effectively reducing the amount available for body functions. Those who have undergone bypass surgery are missing part of their upper intestine which hampers Vitamin D People Taking Certain Medications Steroid Corticosteroid medications used to alleviate inflammation can reduce calcium absorption and impair vitamin D Weight-loss drugs with orlistat (brand names Xenical® and alliTM) and cholesterol-lowering drugs cholestyramine (brand names Questran®, LoCholest®, and Prevalite®) can reduce the absorption of vitamin D and other fat-soluble vitamins.18,19
Medicines used to control and stabalize epileptic seizures, particularly phenobarbital and phenytoin (brand name Dilantin®) interferes with Vitamin D and reduces Calcium absorption.20 Consuming too much vitmain D from food or supplements can lead to anorexia, weight loss, polyuria, heart arrhythmias, kidney stones, and increased risk of heart attacks.5 Vitamin D cannot reach toxic levels if created naturally from sun exposure.21 Oysters, Whole Milk, Salami, Cheese, Caviar, and Eggs are high cholesterol foods which should be eaten in moderate amounts and avoided by people at risk of heart disease or stroke. ReferencesUSDA National Nutrient Database for Standard Reference, Release 28. Office of Dietary Supplements - Vitamin DLong-latency deficiency disease: insights from calcium and vitamin D. Am J Clin Nutr 2003;78:912-9. LeBoff MS, Kohlmeier L, Hurwitz S, Franklin J, Wright J, Glowacki J. Occult vitamin D deficiency in postmenopausal US women with acute hip fracture.
Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.Vitamin D and cancer: current dilemmas and future research needs. Am J Clin Nutr 2008;88:565S-9S. Davis CD, Hartmuller V, Freedman M, Hartge P, Picciano MF, Swanson CA, Milner JA. Vitamin D and cancer: current dilemmas and future needs. Wagner CL, Greer FR; American Academy of Pediatrics Section on Breastfeeding; American Academy of Pediatrics Committee on Nutrition. Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: Exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab 1988;67:373-8. Webb AR, Pilbeam C, Hanafin N, Holick MF. An evaluation of the relative contributions of exposure to sunlight and of diet to the circulating concentrations of 25-hydroxyvitamin D in an elderly nursing home population in Boston.
Am J Clin Nutr 1990;51:1075-81. Lo CW, Paris PW, Clemens TL, Nolan J, Holick MF. Vitamin D absorption in healthy subjects and in patients with intestinal malabsorption syndromes. Am J Clin Nutr 1985;42:644-49. Malone M. Recommended nutritional supplements for bariatric surgery patients. Compher CW, Badellino KO, Boullata JI. Vitamin D and the bariatric surgical patient: a review. Buckley LM, Leib ES, Cartularo KS, Vacek PM, Cooper SM. Calcium and vitamin D3 supplementation prevents bone loss in the spine secondary to low-dose corticosteroids in patients with rheumatoid arthritis. A randomized, double-blind, placebo-controlled trial. Ann Intern Med 1996;125:961-8. Lukert BP, Raisz LG. Glucocorticoid-induced osteoporosis: pathogenesis and management. Ann Intern Med 1990;112:352-64. de Sevaux RGL, Hoitsma AJ, Corstens FHM, Wetzels JFM. Treatment with vitamin D and calcium reduces bone loss after renal transplantation: a randomized study. J Am Soc Nephrol 2002;13:1608-14.