What is Vitamin D?
Vitamin D is not technically a vitamin at all, but rather a kind of hormone that is essential for life. It increases the absorption of calcium from foods in the gut, promotes the healthy growth of bone, and is important for the absorption of iron, magnesium, phosphate, and zinc. It also has beneficial effects on nerve, muscle and immune functions.
Vitamin D deficiency
Normally, Vitamin D is made by your skin following exposure to ultraviolet light in sunlight (UV-B). Overseas, Vitamin D is added to dairy and other foods as a supplement, but in Australia the only mandatorily fortified food in Australia is margarine. Many people have deficiencies due to insufficient sun exposure (due to indoor lifestyles and “Sun Smart” skin cancer prevention) and low dietary intake. During winter in southern Australia (>35ºS in latitude), as much as 58% of the adult population is thought to be Vitamin D deficient. Deficiencies are more common in the elderly population.
In vitamin D deficiency, bones can become thin, brittle, or misshapen over time — classically seen in the diseases rickets (in children) and osteomalacia (in adults). Older adults are particularly at risk of osteoporosis without sufficient Vitamin D and calcium. Improving vitamin D levels in the elderly reduces their risk of falls and bone fractures, through improving balance and strengthening muscles.
Increasing Vitamin D levels using sunshine
The amount of daily sunshine you need on your skin to make enough Vitamin D depends on your skin colour, your location and the season. For moderately fair-skinned people, adequate vitamin D levels may be achieved through summer exposure of the arms (or equivalent) for 6-7 minutes during mid-morning or mid-afternoon. In winter this is increased to 7 to 40 minutes (the longer times are for more southern latitudes) at noon on most days, with as much bare skin exposed as feasible. People with darker skin require exposures that are 3-6 times longer.
Clearly many people cannot receive sufficient sun exposure, especially during a rainy southern winter. For many Australians, supplementation is advisable for at least a part of the year.
Vitamin D supplementation
If you are prone to Vitamin D deficiency, you should have your levels checked every 3-6 months, or as recommended by a doctor.
A daily oral intake of 600-1,000 IU of Vitamin D3 is sufficient for most people, but higher doses may be required in moderate to severe deficiency. Talk to your doctor about high-dose forms of vitamin D taken once a month.
Are there any side effects?
Vitamin D supplementation is very unlikely to cause side effects when used as directed, even with high doses. Side effects that have been reported only very rarely include nausea, vomiting, poor appetite, constipation, weakness, weight loss and kidney damage.
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