Vitamin D – the sunshine factor?

It is the time of the year to relax and get some sun and sand as summer approaches! In Australia, exposure to sunlight is our prime source of vitamin D. When sunlight falls on our skin, a cascade of complex chemical reactions take place on our skin to form vitamin D3 and D2. These vitamins are then transported to the liver and kidney respectively to produce the active form of vitamin D.
Despite our plentiful sunshine, evidence suggests that large numbers of Australians are vitamin D insufficient. In 2007, van der Mei et al., showed in their study amongst Australian women that 40.5% in southeast Queesland, 37.4% in the Geelong region and 67.3% in Tasmania are vitamin D insufficient. This was a shocking revelation! It is estimated that 1 in 5 people in the general community are vitamin D deficient which is much worse than a state of insufficiency! This is because deficiency states lead to rickets (characterised by bow legs and knock knee) in children and osteoporosis and osteomalacia in adults. All these conditions lead to increased risk of bone fracture. Thus the big fallacy that Australians receive adequate vitamin D from casual exposure to sunlight has been dispelled.
In 2007, a study by Creighton University published that a significant supply of vitamin D can reduce the risk of certain cancers by more than 75%. Now, this should make us sit up and take note. Getting sufficient vitamin D can actually save our lives!
The current vitamin D recommendations for Australians are as follow:

1. Infants, children and adults < 50 years – 5 micrograms/day
2. 50 to 70 years – 10 micrograms/day
3. >70 years – 15 micrograms/day
This begs the question, how much sunlight do we actually need? We need approximately 20 minutes sun exposure in winter and 10 minutes in summer, most days of the week, to achieve minimum vitamin D levels. In dark skinned individuals, the length of exposure may even need to be doubled!
Since most of us do not get adequate vitamin D levels from the sun, let’s explore foods sources of vitamin D. Vitamin D is mostly found in fatty fishes, fortified milk, eggs and margarines. The table below lists some of the best food sources:

Food item	Serve size	Vitamin D content (micrograms)
Cod liver oil	1 tablespoon	34
Salmon, cooked	150g	13.5
Mackerel	150g	12.8
Tuna	150g	10.8
Sardines, canned	150g	10.13
Eel	150g	7.4
Prawns	120g	4.5
Milk	1 cup	1.3
Margarine	2tspn	1
Liver	150g	1.2
Egg	1 whole	0.6

With minimal sun exposure, how much vitamin D-rich food must one consume each week to meet minimum vitamin D requirements? Approximately:
• 1 cup of milk/day
• 1-2 teaspoons fortified margarine/day
• 3-4 serves of fatty fish per week
• 3-4 whole eggs each week.
Bon appétit!

References
1. DeLuca HF, Zierold C. Mechanisms and functions of vitamin D. Nutr Rev 1998; 56: S4-S10.
2. Pasco JA, Henry MJ, Nicholson GC, et al. Vitamin D status of women in the Geelong Osteoporosis Study: association with diet and casual exposure to sunlight. Med J Aust 2001; 175: 401-405.
3. Diamond TH, Levy S, Smith A, Day P. High bone turnover in Muslim women with vitamin D deficiency. Med J Aust 2002; 177: 139-141.
4. Dawson-Hughes B, Harris SS, Dallal GE. Plasma calcidiol, season, and serum parathyroid hormone concentrations in healthy elderly men and women. Am J Clin Nutr 1997; 65: 67-71.
5. Koutkia P, Chen TC, Holick MF. Vitamin D intoxication associated with an over-the-counter supplement. N Engl J Med 2001; 345: 66-67.
6. Ingrid A. F. van der Mei, Ponsonby A, Engelsen O, Pasco J, McGrath J, Eyles D., Blizzard L, Hwyer T, Lucas R. The high prevalence of vitamin D insufficiency across Australian populations is only partly explained by season and latitude. Environmental Health Perspectives 2007, 115: 8.
7. Lappe JM, Travers-Gustafson K, Davies KM, Recker RR, Heaney RP. Vitamin D and calcium supplementation reduces cancer risk: results of a randomised trial! American Journal of Clinical Nutrition, 2007; 85: 1586 – 91.