Tuesday, December 21, 2010

Vitamin D

Just like there are trends in TV, fashion and music, there are trends in nutrition. If you have been around for a while then you would have seen a few – fat, fibre, calcium, vitamin C, antioxidants, organic, and the favourite of the last five years has been vitamin D. Getting insufficient vitamin D (primarily through too little sun exposure) has been linked to an increase in an ever-expanding list of medical problems such as heart disease, types 1 and 2 diabetes, multiple sclerosis, depression, colon cancer as well as the well-known problem of osteoporosis (brittle bones).

Institute of Medicine report

Three weeks ago the Institute of Medicine released a new report [http://www.iom.edu/Reports/2010/Dietary-Reference-Intakes-for-Calcium-and-Vitamin-D.aspx] on both calcium and vitamin D. The report re-affirmed that too little vitamin D, along with too little calcium, caused osteoporosis.

The report did increase the recommended daily amounts of vitamin D to Americans and Canadians (previously they were the same levels as Australia) and that increase met with support from academics. However, the report was less enthusiastic about the link with lower levels of vitamin D and common medical problems.

How much vitamin D?

Theoretically you can get all your vitamin D through sun exposure, but many are reluctant to do that for fear of skin cancer. Yet, you don’t need much sun exposure – about 5-8 minutes during the middle of the day (approx 10am – 3pm) in summer, and about 30 minutes in winter for light-skinned people living in temperate zones. In other words, not enough sun to burn, or even get red. Otherwise, you need to get from your diet:

19-50 year olds: 5 mcg (200 IU) in Australia/NZ; 15 mcg (600 IU) in US/Canada; it is assumed you will get adequate sunlight in the UK (insert own gag here).

51-70 year olds: 10 mcg (400 IU) in Australia/NZ; 15 mcg (600 IU) in US/Canada; 10 mcg (400 IU) in the UK

71+ year olds: 15 mcg (600 IU) in Australia/NZ; 20 mcg (800 IU) in US/Canada; 10 mcg (400 IU) in the UK

mcg = microgram;

IU = International Units;

1 mcg = 40 IU

Now, the problem here is that it is virtually impossible to get all your vitamin D needs through healthy eating. Our main sources of vitamin D are margarine (1 mcg in 2 teaspoons), oily fish (about 1-3 mcg per 100g), egg yolk (0.5 mcg per egg) and hard cheese (0.3 mcg in 30g). Some milks are fortified with vitamin D (eg Anlene). You can see you will need to scoff quite a bit of salmon, eggs and margarine to get your D needs. (In the US and Canada there are light-exposed mushrooms that provide 15 mcg/600 IU or more in a single serve. I am working with the mushroom industry in Australia to get high vitamin D mushrooms on the market in 2011).

Blood test

One of the most common blood tests requested is for vitamin D, because so many people appear to be low. How low is low? Mmmm. Tricky question. Last century we thought that a blood level of 25 nmol/L (10 ng/mL) was fine because that seemed to stop rickets and osteoporosis. Now experts like Professor Rebecca Mason from Sydney University say that 50 nmol/L (20 ng/mL) is a better goal for overall health. My pathology test form came back stating that a “healthy” level was 75-120 nmol/L (30-48 ng/mL). There is no universal agreement for the ideal blood levels of vitamin D.

What does it all mean?

Those who get very little sunlight, have dark skin, shield their body from sunlight, are in long term care, or are elderly are likely to have low levels of vitamin D. As diet very probably won’t make up the difference in vitamin D, then daily vitamin D supplements of 25-50 mcg (1000-2000 IU) will need to be taken. Get your blood level tested. If it is clearly at the lower level, get some judicious sunlight, eat wisely, and depending upon where you live, track down some vitamin D mushrooms.

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