THE VITAMIN D DEBATE

As we basked in this summer’s sunshine, Public Health England (PHE) announced that come autumn and winter, we should all start taking vitamin D supplements.

Following PHE’s summer proclamation, we should be tucking into our vitamin D tablets about now. And it certainly was good advice — just arguably rotten timing if PHE wanted us to remember. Perhaps the day the clocks went back would have been better suited to such a seasonal recommendation.

Nonetheless, the advice is based on a 304-page report Vitamin D and Health, by The Scientific Advisory Committee on Nutrition (SACN), which was boiled down into the take-home message: from October to April, everybody should have an average daily intake of 10 micrograms of vitamin D (10 μg/d or 400 IU/d) to protect bone and muscle health, with ‘at risk’ individuals advised to supplement all year round. This is because vitamin D is essential for regulating calcium and phosphorus metabolism, both of which are important for bone health.

But for the British Association for Applied Nutrition and Nutritional Therapy (BANT), which says it has recommended vitamin D supplementation since 1997, the advice is long overdue. BANT’s chairman, Miguel Toribio-Mateas, told Optimum Nutrition: “Despite the fact that it has been clear for 20 years that vitamin D is necessary for muscle and bone health, amended government advice has only just been released.”

He added that if he were a muscle or bone condition sufferer who had not been taking extra vitamin D “that I am only now being told I must take, because PHE’s nutritionists debated whether published evidence was robust enough to recommend supplements, I would be furious”.

However, when reviewed in 1991 by the Committee on Medical Aspects of Food and Nutrition Policy, and then by SACN in 2007, the prevailing thought was that most of us get sufficient vitamin D during the summer when 7-dehydrocholesterol, a form of cholesterol in our skin, is converted into vitamin D3, when we are exposed to sunshine containing ultraviolet B (UVB) radiation.

SACN reported: “It was assumed that skin synthesis of vitamin D in the summer would be enough to cover requirements during the winter.”1 So supplementation was only recommended for ‘at risk’ individuals such as those with dark skin, who needed greater exposure to sunshine, those who covered themselves, or people who were housebound.

But as fear of skin cancer has caused many of us to avoid or block out the sun, a new review was commissioned. SACN, which does not carry out its own primary research, was given the task of reviewing existing studies, and its remit was specific. A statement for PHE said the SACN report “did not look at treating bone or muscle conditions, which would fall to the NHS, rather it looked at vitamin D intake to prevent ill health and such conditions (sic)”. And because of new research looking at other potential benefits of vitamin D, SACN agreed to also look at specific autoimmune conditions.

Bone Health

Once associated with extreme poverty and grim images of bow-legged children, rickets, the disease commonly associated with vitamin D deficiency, is a condition that in the UK was thought to be consigned to history. Children who did not get enough vitamin D in early infancy, or whose mothers were vitamin D-deficient during pregnancy were primarily at risk.

But in recent years, a growing number of cases have been reported particularly (but not exclusively) among communities where it is cultural practice to cover the skin, or in individuals with darker skin. Even in Australia, where there is no lack of sunshine, one study identified vitamin D deficiency with 98 per cent of cases among children with “dark or intermediate skin colour”, with 18 per cent of girls being partially or completely veiled.

In children, rickets causes poor growth and skeletal deformities such as bowed legs, spinal curvature and thickening of the ankles, wrists and knees. In adults, known as osteomalacia, it causes soft bones. Both children and adults may experience pain or tenderness in the bones and muscle weakness.

Non-musculoskeletal Disease

Because of its role as a modulator, there has been a growing view that vitamin D may be beneficial in a range of conditions, including autoimmune diseases (when an over-active immune condition leads to an attack on healthy tissue).

Toribio-Mateas said that emerging evidence suggested a much broader role for vitamin D in immune regulation. “In fact, vitamin D deficiency has been associated as a contributor to the pathogenesis and severity of diverse autoimmune disorders, from autoimmune bowel conditions like coeliac disease to rheumatoid arthritis, lupus, and multiple sclerosis; some of the main reasons individuals seek advice from our members,” he said.

However, given the specific task of looking at the association of low vitamin D levels and the risk of developing specific diseases, SACN found that although low vitamin D serum levels are commonly found in individuals with such diseases, there was insufficient evidence of this being a cause of disease onset. In summary, its report stated that evidence of low serum levels of vitamin D during pregnancy and the development of asthma in offspring was “inconsistent”; that findings from cohort studies of atopic disorders were “inconsistent”; and that a large systematic review of 219 studies (intervention, prospective and cross-sectional) found that vitamin D supplementation had “little effect on risk of developing autoimmune disease”.

SACN also reported that there was “a paucity” of randomised controlled trials (RCTs) on the effect of vitamin D supplementation on development of specific autoimmune diseases; that evidence linking vitamin D and multiple sclerosis was “largely observational and inconsistent”; and that in the case of vitamin D and type 1 diabetes, inflammatory bowel disease, rheumatoid arthritis and SLE (lupus), data were “lacking”.

Direct cause and effect was, therefore, not considered to have been established. While low vitamin D levels were associated with certain autoimmune conditions, SACN stated that this could even be due to “reverse causality” — in other words, rather than low vitamin D serum levels causing the illness, the illness may be affecting vitamin D serum levels.

Explaining SACN’s approach, Dr Louis Levy, head of nutrition science at PHE, said: “Our independent experts review all the available evidence — often thousands of scientific papers — run full-scale consultations and go to great lengths to ensure no bias.”

However, Toribio-Mateas said: “If we wanted to avoid the word pathogenesis, we could use the phrase ‘disease activity’, which appears in several trials... several studies have found an association between vitamin D deficiency/insufficiency and disease activity in individuals suffering from inflammatory and autoimmune bowel disease, etc.”

Again, it is important to emphasise that association is not cause, but Toribio-Mateas cites as examples studies in which vitamin D supplementation has a reported association with improved symptoms; one being a review of psoriasis and another a study into Hashimoto’s thyroiditis. These alone may not be enough on which to base a public health policy, but could indicate that the chapter on vitamin D and autoimmune disease may not yet be fully written.

The Biology

Our bodies need vitamin D to absorb dietary calcium. If we don’t get enough, we absorb less of the calcium that we eat, and our body leaches calcium from bones and directs it to the heart and nerves, where it is vital — because when it comes to survival, a functioning heart is more important than healthy bones.

But vitamin D’s function is believed to extend far beyond this, as it has been discovered that many tissues in organs such as prostate, heart, blood vessels, muscles and endocrine glands contain proteins (receptors) that bind to vitamin D.

Asthma

The importance of vitamin D beyond bone health is something that may have been recently illustrated in a study led by Queen Mary University of London (QMUL), which found that vitamin D supplementation reduced the risk of severe asthma attacks. Vitamin D was not suggested as a cure for asthma, nor said to affect day-to-day symptoms; only to reduce the risk of an attack that might need hospitalisation and to reduce the need for systemic steroids.

The news was welcomed by BANT, although the report’s authors have treated their findings with caution. Not only did the findings relating to severe asthma attacks came from just three trials, but most of the subjects were adults with mild or moderate asthma. Because of this, the authors stated that further trials in children and in adults with severe asthma were needed.

What it does show, however, is that as new research challenges existing thought, the debate over autoimmune disease and vitamin D is likely to continue.

Recommendations

To repeat the PHE/SACN message, the current recommendation for vitamin D is that within the UK (and likely all other countries on the same latitude), we should all be supplementing our vitamin D intake to maintain musculoskeletal health.

A nutritional therapy approach, particularly for post-menopausal women, would also be to recommend vitamin K2, which has been shown to be equally important for bone health, with studies reporting that it may help slow down osteoporosis.

But regardless of any debate, if taking vitamin D as PHE advises can also benefit other areas of our health, then that can only be an added bonus.challenges existing thought, the debate over autoimmune disease and vitamin D is likely to continue.

By Louise Wates in "Optimum Nutrition", Autumn 2016,UK, excerpts pp.18-19. Adapted and illustrated to be posted by Leopoldo Costa.

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