According to MICHAEL F. HOLICK, MD, PhD, arguably the world’s leading authority on vitamin D, about 50% of the population in Canada and the US are getting get too little vitamin D. This is true even in sunny climates, because of lack of sun exposure.
Vitamin D regulates calcium and phosphorus levels and promotes absorption of these minerals for growth of bones and teeth. It is also involved in insulin secretion, supports immune function and regulates blood pressure. It is used to prevent and treat osteoporosis, psoriasis, autoimmune disease, and to reduce the risk of cancer.
Vitamin D can be produced in the skin upon exposure to sunlight or must be obtained from the diet. Vitamin d deficiency symptoms occur with inadequate dietary intake, limited sun exposure, kidney or liver disease, and alcoholism. Elderly, dark-skinned, obese people, or those with inflammatory bowel disease and fat-malabsorption syndromes (celiac disease and cystic fibrosis) are also at greater risk. Ten to fifteen minutes of sun exposure at least two times per week to the face, arms, hands, or back without sunscreen is usually sufficient to provide adequate vitamin D.
Vitamin d deficiency symptoms include: rickets (weak, deformed bones) in children, osteomalacia (soft bones) and osteoporosis in adults, dental problems, muscle weakness, and tooth decay.
Drugs that deplete vitamin D include: carbamazepine, phenytoin, phenobarbital, cimetidine, ranitidine, cholestyramine, colestipol, orlistat, and mineral oil.
Since vitamin D is found in few foods and at low amounts, a supplement is recommended for most people. Most multivitamins provide 400 IU (10 mcg), however the Canadian Cancer Society recommends a daily intake of 1,000 IU for adults in the fall and winter. The Canadian recommendation reflects the fact that there is reduced sun exposure in northern latitudes. The recommendation is for 1,000 IU intake year-round for people who are older, have dark skin, don’t go outside often, or wear clothing that covers most of their skin. Also,people with limited sun exposure, osteoporosis, multiple sclerosis, psoriasis, and those over age 65 should consider additional vitamin D.
Food sources of vitamin D include: Fatty fish (mackerel, salmon, sardines), fish liver oils, eggs from hens fed vitamin D, and milk.