Vitamin D is found in dietary sources such as fatty fish, eggs, and fortified milk. The sun also contributes significantly to vitamin D production. As little as ten minutes of exposure is thought to be enough to prevent deficiencies. There are several forms of the vitamin, two being important for humans: One is Ergocalciferol (vitamin D2) and the other is Cholecalciferol (vitamin D3). D2 is synthesized by plants. D3 is synthesized by humans in the skin when it is exposed to ultraviolet B (UVB) rays from sunlight. Foods may also be fortified with vitamin D2 and D3.
The main reason we need vitamin D is to maintain normal blood levels of calcium and phosphorus. Vit D aids in the absorption of calcium, which helps keep bones and muscles healthy and strong, as well as preventing osteoporosis. By itself, vitamin D doesn’t do much. Its main purpose is to assist in specific functions of the body or to prevent certain processes. For example, Calcitonin, a hormone released by the thyroid gland, can cause cartilage to degenerate if vitamin D doesn’t inhibit this process.
Falls are the second leading cause of death in the United States with 75% of those falls occurring in the elderly. In long-term care, we are increasingly interested in preventing rehospitalizations for any reason. Can vitamin D prevent fractures and subsequent hospitalization in the elderly? Quite a few studies of late, nearly a dozen, indicate that yes, vitamin D in daily doses of 800 IU does consistently prevent fractures. A dose that high has been found to reduce the risk of hip fractures by 30% and other breaks by 14%. However, lower doses did not have any effect.
In an article from Mayo Clinic, vitamin D is mentioned in association with many medical issues including hyper and hypoparathyroidism, fall preventions, muscle weakness or pain, osteoporosis, asthma, chronic kidney disease, cancer prevention (breast, colorectal, prostate, other), cardiovascular disease, cognition, fracture prevention, fracture treatment, hyperlipidemia, hypertension, mood disorders and mortality reduction.
Some causes of vitamin D deficiency include not eating recommended levels of the vitamin over time, limited exposure to sunlight as in many nursing homes or dark skin. As people age their kidneys are less able to convert vitamin D to its active form.
How much is enough and how much is too much? Since vitamin D is a fat-soluble vitamin, toxicity is possible and too much can actually inhibit calcium absorption. Guidelines from the Institute of Medicine increased the recommended dietary allowance (RDA) of vitamin D to 600 international units (IU) for everyone aged 1-70, and raised it to 800 IU for adults older than 70 to optimize bone health. The safe upper limit was also raised to 4,000 IUs.