Last Saturday the Times newspaper here in the UK carried a piece I’d written summarising some of the most salient issues regarding vitamin D deficiency and what we might do about it. Here it is…
The shortened days at this time of year will for some people usher in a downturn in mood that may culminate in full-blown depression. However, research also suggests that the winter months pose other hazards to health linked to the bottoming out of vitamin D – a critical nutrient made in the skin through the action of sunlight. Recently published research connecting lower light exposure and depressed vitamin D levels with impaired fertility in women undergoing IVF. This research, though, is just the tip of the iceberg of evidence linking higher vitamin D levels with a glowing array of benefits for health.
There exists, for example, a wealth of research linking sunlight exposure with relative protection from several different forms of cancer. A review published earlier this year in the journal Anticancer Research found greater exposure to the sun to be strongly associated with a reduced risk of 15 different types of cancer including those of the breast, colon, bladder and cervix.
Yet, when sunlight is mentioned with regard to cancer, its relationship with skin cancer tends to put it in a negative light. Higher levels of sun exposure are indeed strongly linked with the relatively harmless non-melanoma skin cancers (known as squamous cell and basal cell cancers), as partly evidenced by the fact that these cancers usually crop-up on sun-exposed parts of the body such at the face and back of the hands. However, the link between sunlight exposure and the much more deadly malignant melanoma is not clear-cut, with most of these occurring in not typically sun-exposed parts of the body. Also, indoor workers are at increased risk of melanoma compared to outdoor workers, and some studies link higher levels of sun exposure with lower melanoma risk.
However, even if we assume that sunlight exposure is a potent factor in melanoma, the evidence shows that greater sun exposure is linked with protection from cancer as a whole. This evidence should remind us that when advising about any lifestyle factor, we should take as broad a view as possible and not confine ourselves to one condition (skin cancer).
Evidence linking sun exposure with a reduced risk of heart disease tips the balance further in sunlight’s favour. VitaminD may lower blood pressure, at least in part through it’s ability to influence blood-pressure determining hormones such as renin. Also, a basic chemical building block of vitamin D is cholesterol, and sunlight therefore has some capacity to lower cholesterol levels by catalysing cholesterol’s transformation into vitamin D. This has led some to suggest that ‘raised’ levels of cholesterol may be the result of ‘sunlight deficiency’. Vitamin D is also known to have natural anti-inflammatory actions in the body, which has relevance as inflammation has emerged as an important underlying mechanism in atherosclerosis (the ‘gumming up’ process on the inside of the arteries which can lead to heart attacks and strokes). In one study published in the Archives of Internal Medicine in 2008, men with levels of vitamin D < 15 ng/ml (see below for more on levels) were more than twice as likely to suffer a heart attack compared to those with levels > 30 ng/ml.
Other research links sunlight exposure and heightened vitamin D levels with relatively protection from auto-immune diseases – those conditions in which the body’s immune system is reacting against its own tissues. One example of this is the neurological condition multiple sclerosis, the incidence of which is close to zero in equatorial regions and but increases steadily the further one gets from the equator.
As voluminous as the research revealing links between sunlight, vitamin D and improved health is, it’s important to bear in mind that this work is ‘epidemiological’ in nature. This sort of evidence may reveal associations between things, but that does not necessarily mean one is causing the other. To establish a ‘causal’ link between these things and demonstrate that vitamin D is disease protective we require what are known as intervention studies. Here, individuals are treated with vitamin D, and the outcomes are compared with those taking a placebo (dummy pill).
Such studies require considerable manpower and funds, and perhaps as a result there’s a relative dearth of them. The studies that do exist can be somewhat limited in their usefulness partly because the dosages used in them are often insufficient to optimise vitamin D levels, as well as their relatively short duration (it may take many years for the beneficial effects on conditions such as heart disease and cancer to becomes apparent). However, even with these limitations there have been some encouraging findings, with a major review published in the Journal of Clinical Endocrinology and Metabolism in August of this year
finding that supplementation with vitamin D along with calcium (though not vitamin D alone) for an average of 3 years reduced overall risk of death by 9 per cent.
Other evidence has found that vitamin D alone has potential as an antidepressant. In one study published in the Journal of Internal Medicine in 2008, vitamin D therapy was found to improve the symptoms of depression compared to a placebo. In clinical practice, I have found that optimisation of vitamin D is often very beneficial for reducing or even eliminating the symptoms of ‘season affective disorder’ (winter blues), which suggests that this condition may be caused, at least in part, by low vitamin D levels at this time of year.
The role of vitamin D in physical and mental health has risen up the agenda in recent years, and a driving factor has been the growing recognition of widespread deficiency in some countries including the UK. In recent times we have heard doctors alerting us to a resurgence of rickets (malformed and weakened bones as a result of vitamin Ddeficiency) in the UK.
The only way to know for sure whether the body has sufficient levels of vitamin D is via blood testing. However, even here it needs to be borne in mind that references ranges are set on a largely deficient population, which means ‘normal’ ranges do not represent optimal levels for health and wellbeing.
My preference is for levels to be around 50 ng/ml = 125 nmol/l (toxicity does not appear to occur at levels under 200 ng/ml). Yet, evidence suggests that in the UK, approaching 90 per cent of 45-year-olds will have levels lower than 30 ng/ml in the winter, though in the summer and autumn, still about 60 per cent fall into this category. Bearing in mind the research linking higher vitamin D levels with benefits for a range of health parameters, it may well be that generalised vitamin D deficiency is contributing to the disease burden in the UK.
The research on vitamin D levels quoted above was conducted in Caucasians and the relevance of this is that, for a given amount of sunlight, fairer skins generally make more vitamin D than darker ones. What this means is that vitamin D deficiency is likely to be even more prevalent in those of Asian and Afro-Caribbean decent. Those living at more northerly latitudes are also at increased risk of vitamin D deficiency, as are those whose exposure to sunlight is limited (such as the elderly).
Vitamin D levels can be improved with sunlight exposure, but it should be borne in mind that when the sun is low in the sky, vitamin D cannot be made in the skin. As a general rule, in the UK vitamin D can only be made from the end of March through to September, and only in the middle of the day. A decent rule of thumb is that good vitamin D-generating potential is to be had when one’s shadow is shorter than one’s height. While it is important not to allow the skin to burn, even 10 or 20 minutes of daily sun exposure (without sunscreen) to bare legs, arms and torso can do much to boost vitamin D levels.
Boosting levels in the summer will help build up vitamin D stores that may help tide us through the winter. Another approach is to increase our consumption of vitamin D-rich foods such as oily fish. However, the amount of vitamin Dfound in food generally pales into insignificance compared to the amount we can make from sun exposure and is generally required for optimal levels of vitamin D in the body.
Vitamin D supplementation represents a practical option, and dosages required to make significant difference to bloodvitamin D levels are usually in the order of several thousand international units (IU) per day. In practice I’ve found that about 1,000 IU (25 micrograms) of daily supplementation with vitamin D3 usually raises blood levels by 10 ng/ml (25 nmol/l) over time.
Children, just like adults, need vitamin D too, something that is highlighted by the recent resurgence in rickets. Again, ideally levels should be checked, but approximate appropriate supplementation levels are 1,000 IU for children under the age of 1 year, and 1,000 IU for each 25 lbs (11 kg) of body weight for older children. Pregnant women in the UK are recommended to supplement with 400 IU of vitamin D each day as a matter of course.