Vitamin D helps both the intestines absorb dietary calcium into the blood and bones utilize the blood calcium. The dietary sources of Vitamin D are derived mainly from egg yolks, fatty fish (mackerel, salmon, tuna) and beef liver. Some foods are fortified with vitamin D (and it says so on the label): milk and other dairy products, cereals, grains and orange juice. Our skin when exposed to the sun’s ultraviolet B rays also absorbs Vitamin D. It takes as little as 30 minutes of regular sun exposure twice a week to give us the vitamin D we need. Vitamin D in food and supplements is an inactive pro-hormone; it is converted by the liver and kidneys into the metabolically active hormone, calcitriol. Calcitriol interacts with most body cells via specific receptors, much like a key unlocks a door, to allow something to happen. Interaction with muscle receptors, for example, promotes muscle strength and balance whereas interaction with bone receptors promotes bone strength. The reverse is also true; a deficiency of vitamin D, among other things, impairs bone and muscle health, causing an increase in falls and fractures.
It is clear that treating people with calcium and vitamin D deficiencies is important but what is not clear is whether giving the usual doses of vitamin D plus calcium to independent people who have never had a fracture helps prevent problems. The available data on giving the combination of calcium plus vitamin D to healthy people, as reviewed by the United States Preventive Service Task Force (USPSTF), not only says that it does not prevent osteoporosis and fractures, but also says that it may even cause harm. The USPSTF review did not examine calcium supplementation without vitamin D because most people take the two together and not enough people take calcium on its own.
The studies looked at a most vulnerable segment of the population, i.e. independent, post-menopausal white women, because they have the highest rate of osteoporosis and fractures. Hence, the conclusions only apply to that group and not to men and pre-menopausal women (who are at a much lower risk for osteoporotic fractures) or to the institutionalized elderly (who are at a much higher risk for osteoporotic fractures). Also the conclusions did not take into consideration the benefits and harms of daily supplements larger than the commonly used doses of 400 units of vitamin D and 1000 mg of calcium because of insufficient data, leaving the issue to be clarified by future studies, which should tell us whether taking calcium or vitamin D supplements is helpful or harmful.
Consequently, the USPSTF recommends against daily supplementation with 400 IU or less of vitamin D and 1000 mg or less of calcium for the primary prevention of fractures in independent, post-menopausal women. In a previous publication, however, it did recommend vitamin D supplementation (without calcium) for the prevention of falls in those independent adults aged 65 or older who are at an increased risk of falls.
Fractures, whether treated or not, cause chronic pain, disability, dependence, decreased quality of life and high mortality. During their lifetime, 50% of postmenopausal women will suffer an osteoporotic fracture and about 1.5 million osteoporotic fractures per year occur in the US alone. In the first 3 months after a hip fracture, a person’s mortality increases by 3 to 4 times and 20% are subsequently institutionalized.
The USPSTF recommends screening for osteoporosis in women aged 65 or older, as well as in women of any age if they have disorders associated with high risk for osteoporosis.
Supplementation with common doses of vitamin D and calcium increases the incidence of kidney stones. In the Women’s Health Initiative study, one woman suffered a kidney stone for every 273 women who received supplementation over a period of 7 years. Supplementation with calcium alone may also increase heart attacks by causing calcifications of coronary arteries, but this data is observational and have not been verified by prospective, controlled studies. Unlike supplements, dietary calcium does not cause coronary calcifications and is thus preferred.
Vitamin D, besides helping bones and muscles, may have several other benefits. Helping the immune system fight viral infections and reducing the chance of certain neurological disorders, certain cancers and certain cardiovascular diseases are among its purported benefits but prospective, controlled studies are currently lacking. Those who don’t get enough sunlight, taking about 1000 units of vitamin D per day is more than enough as doses over 4000 units/day could prove toxic to heart, kidney and brain. Checking vitamin D blood level is seldom necessary in most healthy people.
Before taking any supplement, one should check that the United States Pharmacopeia (USP) has verified it. If the supplement displays the (USP) label, it means that it is free of impurities and contains exactly what its label says. Supplements without the (USP) label may contain harmful impurities and may have greater or lesser amounts than their labels say.
Regular exercise, reasonable sun exposure, healthy diet, not smoking, and avoiding excess alcohol are far more important than supplements for the maintenance of good health and well-being.