Vitamin D In Winter

Written by Miranda Bone (Bachelor of Human Nutrition, University of Canberra)

Brrr! Who else has been rugging up to withstand the cold? And did anyone get 20 minutes of sunshine to their face, arms and hands? Sunshine is used by the body to make vitamin D, and in winter, most of us do not get enough. We can get some vitamin D through diet – vegetarian sources are fortified non-dairy milks and margerine (eg.  Nuttelex) – however we get most of our vitamin D from the sun.

Vitamin D is known for its role in calcium metabolism. It helps us absorb calcium from our foods, and stops us excreting so much calcium. Because calcium (along with other minerals) helps make strong bones, it is important for bone health to have sufficient vitamin D. Enough vitamin D means we don’t need to eat quite as much calcium – important for anyone eating less dairy! Also, recent research suggests getting plenty of vitamin D may help prevent heart disease and cancer, and there’sa possible link to Multiple Sclerosis and Schitzophenia as well (1-4).

So how much vitamin D is enough, and how can we get it? Well, the NHMRC recommends we include 5 ug/day in our diets if we are not getting much sun (or 10 ug for those aged 51-70; 15 ug for those older than 70). We can get that from fortified foods (check labels of milk, and soymilk; note Nuttelex has 0.5 ug per serve) or from supplements. Supplements may or may not be animal derived: D3, or cholecalciferol is from lanolin (from wool); D2, or ergocalciferol, can be derived from animal or plant sources. The animal version, D3, is more potent, but the body is able to activate D2 in the liver and kidneys, to produce active vitamin D.

The sun is also a source of vitamin D – our body is capable of making enough vitamin D from sunlight alone. However, because of the risk of skin cancer, be sensible about it! The skin stops making vitamin D before you burn; aim for about 1/3 as much time in the sun as it would take you to get slightly pink. That varies with time of day, the weather, and your skin colour, but for fair skinned people in a Canberra winter, about 30 minutes in the morning or afternoon is about right, less if you’re sunning yourself at lunch time. If you’re going to be in the sun longer than that – slip slop slap! If you have trouble getting enough sun, do consider using fortified foods or supplements.

1. Wang TJ, Pencina MJ, Booth SL, Jacques PF, Ingelsson E, Lanier K, et al. Vitamin D deficiency and risk of cardiovascular disease. Circulation. 2008 January 29;117(4):503-11. 2. Giovannucci E. Vitamin D and cancer incidence in the harvard cohorts. Annals of Epidemiology. 2009;19(2):84-8. 3. Cantorna MT. Vitamin D and multiple sclerosis: An update. Nutrition Reviews. 2008;66(s2):S138-. 4. McGrath J. Hypothesis: Is low prenatal vitamin D a risk-modifying factor for schizophrenia?  Schizophrenia Research. 1999;40(3):173-7.

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