Bring on the sunshine
Much of the research in this area has focussed on the hazards of over-exposure to sunlight, and its confirmed association with increased skin cancer risk — a big concern for pale-skinned populations like the indigenous Irish.
But little consideration has been given to the things we might be missing out on if we (correctly) limit our exposure to sunshine over the summer months.
As well as being found in the diet, vitamin D is unique in that it can be made in our skin under the influence of direct sunlight. And in recent years, we’ve begun to recognise that completely avoiding sunlight can seriously deplete our levels of this critical nutrient. Intakes of vitamin D from food average just 3-4 micrograms per day in Ireland, in contrast to the 70-125 micrograms we typically generate when our skin’s exposed to sunshine on a warm summer’s day.
In the past this worked seamlessly — we worked and played outdoors during the bright summer months, and made lots of vitamin D which got stockpiled in our liver and fat tissue for later use over the dark winter months. In this scenario, the low amounts of vitamin D we got from our diet were useful, but only to delay the decline in our body stores of this nutrient as we progressed though winter. These dietary intakes were quite incidental — the main determinant of our vitamin D levels by late winter was the amount of the vitamin we’d managed to generate and store in our body the previous summer.
With the movement of life indoors over the past 30-40 years all this has changed.
Many of us work long hours in offices and factories, venturing out in summertime only after the liberal application of high-strength sun block. Our recent dismal summers have exacerbated this problem, meaning that the vast majority of us fail to “re-stock” this vital nutrient during summer in the way that we used to.
This isn’t to say that people should increase their exposure to sunlight. The critical point is that reduced sunlight exposure creates a deficit in vitamin D that has to be derived from another source.
Evidence of insufficiency has been observed across the length and breadth of Ireland. As far back as 2006, researchers in Cork showed that 34-85% of Irish women and roughly one in three Irish men had inadequate vitamin D levels in late winter. Statistics from last year indicate that 40% of Irish adults have inadequate vitamin D levels, rising to 55% during the dark winter months.
There are many people who think this is all a lot of bluster about nothing — they’re wrong.
Before the early ’90s, it was assumed that if you didn’t have rickets or osteomalacia, rare skeletal disorders characterised by soft, pliable, painful bone, that you had sufficient vitamin D.
Then it was discovered that low vitamin D levels contributed to osteoporosis, a much more common bone disorder which occurs “silently” in older adults (especially women) and vastly increases their risk of hip, wrist and spinal fractures.
More recently, low vitamin D levels have also been implicated in the development of cancer (especially gut cancers), high blood pressure, heart disease, diabetes and several auto- immune disorders, including multiple sclerosis, rheumatoid arthritis and Crohn’s disease. All of these are very common in Ireland, and impose considerable treatment costs.
Since 2011, the Food Safety Authority of Ireland has recommended we take a daily vitamin D supplement — 5 micrograms for those aged five to 50 years, and 10 micrograms for those aged over 50. Disappointingly, research from last year shows that just one in six of the adult population are following this advice, suggesting that food fortification with vitamin D may be more effective.
If you’re concerned about your vitamin D level, ask your GP to test it, and to recommend a suitable supplement if required.
* Dr Daniel McCartney, Lecturer in Human Nutrition & Dietetics at DIT
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