Thursday, December 15, 2011

Vitamin D

Last month I was very lucky to be the minder for Michael Holick, professor of medicine from Boston University during his seminar series on vitamin D in Sydney and Melbourne, Australia. Want to learn fast? Book a professor for four days. They are very clever people.

Every cell has a vitamin D receptor
Michael is a world expert on vitamin D. Just to remind you how young the science of nutrition really is, know this: he discovered the circulating form of vitamin D as a Masters student. This is the same form that is measured when you have a blood test for your vitamin D status.

In my youth way back I took cod liver oil by teaspoon to avoid rickets. Will never forget the taste. Now, vitamin D has gone beyond bendy bones. Nearly every cell in your body has a vitamin D receptor. Over 2000 genes are influenced by vitamin D. No surprise that a lack of D has been linked to major conditions from Multiple Sclerosis, heart disease, bowel cancer and breast cancer to diabetes, the flu and depression.

Kellie Bilinski, an Australian breast cancer researcher told me that D regulates about 200 genes in breast cancer cell production and low D was directly related to a higher risk of breast cancer.

Is there a vitamin D problem in Australia?
Yes, for two main reasons. First we have been discouraged to expose our skin to sun during the daylight hours when our skin makes vitamin D in response to the UV rays, mainly due to the realistic fear that we may get skin cancer. The avoidance of the sun by mothers and infants has seen the re-emergence of rickets in Australia.

Secondly, for many there is little opportunity to venture outside during working hours. Three out of 10 healthy Sydney office workers have low vitamin D in the summer. They couldn’t even boost their vitamin D over the weekends. Three in four healthy dark-skinned Australians are D deficient in the winter (I might add, that is common around the world. Michael Holick had just been to India where D deficiency is rife).

I have specified “healthy” people because we assume they can get outside of their own choosing. There are much higher levels of D deficiency in the elderly and unwell. Around three quarters of hospital inpatients are D deficient.

For every 10 nmol/L (25 ng/mL) our D levels rise, there is a 6-8% reduced risk of early death, possibly due to a reduced chance of cancer.

What does it all mean?
First, get your vitamin D levels checked. They will be lowest in September and highest in March in the southern hemisphere; vice versa in Europe and North America. Although there is debate as to the “healthy” blood level of D, every expert is saying you should have at least 50 nmol/L (125 ng/mL), although Michael Holick believes you are better off at 75 nmol/L (187 ng/mL). If we use the latter figure then Dr Rob Daly from Deakin University says that 73% of Australian don’t make the grade.

You will only reach healthy levels of D by getting a judicious exposure to sunlight or taking supplements of 50 mcg (2000 International Units) of vitamin D.

It is very difficult to get enough vitamin D from food alone. Most researchers now agree that you will need to eat 15 mcg (600 IU) a day. With table margarine providing 1 mcg per two teaspoons, oily fish 2 mcg per 100g, D-fortified milk with 1-4 mcg per glass you can see it will be tricky getting your 15 mcg a day. Only one food can provide your daily needs of D in a serve and that is light-exposed mushrooms, but they are only available from some Sydney grocers, although they have been in the US and Canada for a couple of years.

A final thought from Michael Holick. Why did the dinosaurs die 65 million years ago? No brainer. It was vitamin D deficiency caused by the asteroid dust cloud blocking out the sun. Want more? Watch his quick-fire presentation.

No comments: