| Vitamin D is a vitamin that’s hard to get from food. We’re designed to make vitamin D in our skin when we are out in the sun and, in our hunter-gatherer past, we would have had no problem making ample amounts. In those days, if you made enough in summer, it was stored in your body to tide you over the winter months when the sun’s rays were too weak to trigger skin production.
When you expose your skin to the sun, a cholesterol metabolite naturally found in your skin is converted into vitamin D and sent to the liver for storage. Stored vitamin D is released as needed and sent to the liver for conversion to the active form. Active vitamin D’s main function is to maintain your body levels of calcium to support your bones, teeth, muscles, and nerves. The latest research on vitamin D is showing that it has a much wider range of actions than previously believed, including helping to regulate cell division and maintaining the health of the skin, joints, cardiovascular system, and immune system.1
How much sun is enough?
Strangely enough, you make vitamin D when you’re exposed to the burning UVB rays of the sun but luckily you don’t have to risk sunburn to get it. It’s best to get out in the sun before 10 am or after 2pm during the summer months and about 6-8 minutes of exposure of most of your body should be enough, if you’re fair-skinned, to start the process of making vitamin D.2 This will then continue when you cover up or go indoors.
Getting enough vitamin D is not easy
Clothes and sunscreens have a blocking effect so, for better vitamin D levels, cover up or apply sunscreen after you’ve been in the sun for the few minutes needed to kick-start vitamin D production. It’s harder for the sun’s rays to penetrate pigmented skin and people with dark skin may require 10-50 times more exposure to UVB compared to those with light skin.1 As we age, our ability to make vitamin D and absorb it from food decreases.1
Summer sun is important because, the further away from the Equator you live, the less vitamin D you make in winter. At latitudes above 35º, the angle of the sun is so oblique in winter that UVB radiation in the right wavelength for making vitamin D can’t reach the skin.1 Adelaide is located at 34º latitude, Melbourne is 37º and Hobart is 42º, so winter sun exposure is not going to help boost your vitamin D levels if you live in these localities.
The sunny country is now the sun-starved country
Vitamin D deficiency is becoming more common in Western countries and our lifestyle has a lot to do with it. We live a much more indoor life than in the past and ‘sun phobia’ is on the rise; some people cover up or use sunscreens year round because of concerns about skin damage and premature ageing. A factor 8 or 15 sunscreen, properly applied, reduces the skin’s ability to make vitamin D by 95% and 99% respectively.3
Vitamin D deficiency is much more common in Australia and New Zealand than previously believed. Both dietary intake of vitamin D and sun exposure are inadequate in many Australians and low vitamin D status is common over a wide latitude range.4 Surprisingly for such a sunny region, a study of Queensland people found that 42% had low blood levels of vitamin D at the end of winter.5 In Australia, low vitamin D levels are more common in dark-skinned veiled pregnant women, mothers of infants treated for rickets, and elderly nursing home and hostel residents. Somewhere between 23% and 43% of younger adults may have marginal deficiencies.6
What are the best food sources?
Most foods are poor sources of vitamin D. Richest sources are fatty fish, shellfish, meat, milk, eggs, butter, cream, and fortified foods such as fortified milk and margarine but the amount of dietary vitamin D is extremely low compared to the amount normally made in the skin. Fish liver oils are a useful source but may provide more vitamin A than is desirable. Standard fish oil supplements contain very little vitamin D.
How much vitamin D do you need?
The Australian government guidelines state that an adequate intake of vitamin D is 5-15 mcg (200-600 IU) a day for adults, assuming some sun exposure.7 Other researchers have recommended that, for good health, the daily supply of vitamin D from all sources should be greater than 20 mcg (800 IU).8 In a severe deficiency, Australian and New Zealand authorities recommend supplements of 5,000 to 10,000 IU (125 - 250 mcg) daily for about three months until blood levels are restored to normal.2 As many of us don’t get enough sun, a supplement of 1,000 IU a day can help to maintain healthy body levels.
Can you overdo vitamin D supplements?
Doses of 600,000 IU (15 mg) of vitamin D have been given by injection once yearly without harmful effects.2 According to research, there is no evidence of adverse effects at blood levels up to 140 nmol/L and to get to this level, you would need to have a total intake of about 250 mcg (10,000 IU) a day.8
References
1. Holick MF. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Am J Clin Nutr. 2004 Mar;79(3):362-71.
2. Osteoporosis Australia and the Australian and New Zealand Bone and Mineral Society. Recommendations from the vitamin D and calcium forum. Medicine Today. 2005. 6(12):43-50.
3. Matsuoka LY, Ide L, Wortsman J, et al. Sunscreens suppress cutaneous vitamin D3 synthesis. J Clin Endocrinol Metab 1987;64:1165–8.
4. van der Mei IA, Ponsonby AL, Engelsen O, et al. The high prevalence of vitamin D insufficiency across Australian populations is only partly explained by season and latitude. Environ Health Perspect. 2007 Aug;115(8):1132-9.
5. Kimlin M, Harrison S, Nowak M, et al. Does a high UV environment ensure adequate vitamin D status? J Photochem Photobiol B. 2007 Dec 14;89(2-3):139-47.
6. Nowson CA, Margerison C. Vitamin D intake and vitamin D status of Australians. Med J Aust. 2002 Aug 5;177(3):149-52.
7. Australian Government, Department of Health and Ageing, National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand. 2005.
8. Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr. 1999 May;69(5):842-56.
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