Not such a sunny outlook

WE may dream of a sun-filled Irish summer but the reality is usually bleaker — drizzle and overcast skies. There’s now reliable research which indicates that Ireland’s dull environment might have a greater impact on health than we imagine. This all relates to vitamin D, a “hormone-vitamin” derived mainly from the action of sunlight on our skin over the summer months.

While most of us are aware of the increased risk of cancer with over-exposure to sunshine, less of us realise that the vitamin D we make in response to sunshine may protect against this deadly disease.

This first came to light when US scientists noticed that certain cancers were much more prevalent in areas which got less sunshine. At first, this appeared to be an artefact — after all, people in sunnier climates probably take more exercise and eat more fresh fruit and vegetables than their sun-starved peers. However, it later became clear that the positive benefits of sunshine persisted, even after adjustment for these other factors.

At this stage, the laboratory scientists got to work to determine why sunlight exposure might have this effect, and slowly but surely, several mechanisms by which vitamin D inadequacy influences cancer risk began to emerge.

These findings were unexpected, but profound. For example, low vitamin D levels were found to contribute to inflammation, a potent risk factor for several cancers. They were also found to affect normal cell development and programmed cell death, two critical elements in tumour development.

Currently, Ireland has extremely high cancer rates in comparison to other countries. Our men lie third in the world tables behind France and Australia, with our women a close third behind Denmark and New Zealand. To put this in context, our overall cancer rates are roughly 75% higher than the averages observed among even the top 50 countries, with cancers of the throat, colon, prostate, lung and breast particularly prominent. This is pertinent as all of these cancers have been linked to low vitamin D status.

Dietary vitamin D intakes are also very low in Ireland, with average intakes for adults estimated at 3-5 micrograms per day. Even though poor dietary intakes also prevail in other countries, many of these places also receive plenty of sunshine to make up that shortfall.

Ireland doesn’t have this luxury. The low and unreliable levels of sunshine in summer are compounded by our indoor lifestyle and zealous use of sun-block. Unsurprisingly given these trends, blood levels of vitamin D are lamentably low right across the Irish population, especially common among older women, dark-skinned ethnic minorities and the obese.

So what’s to be done? Well, there are legitimate concerns about increasing sunlight exposure due to its proven links with skin cancer. The addition of vitamin D to foods is another option, but one which has several challenges. The third option is supplementation. Several studies in the US have suggested that if the entire US population to take an extra 25 micrograms of vitamin D each day (a level not achievable by diet), overall cancer rates would drop by 15-20%, with deaths from gut cancer falling by as much as 45%. Those are persuasive odds against a pervasive and deadly foe, so although it’s not the only preventive measure to be taken, vitamin D supplementation certainly looks like a promising weapon in Ireland’s ongoing fight against cancer.