Vitamin D, often affectionately labelled the sunshine vitamin, has been supported by doctors, patients and the media for decades. As well as tackling vitamin D deficiencies, it has many benefits when it comes to heart disease, diabetes and can reduce the onset of conditions such as dementia and cancer. The vitamin also helps to control levels of calcium and phosphate in the blood and is essential for the formation of bones and teeth.
Sources of Vitamin D include oily fish and eggs, but it can be difficult to get enough through diet alone. Most people generate vitamin D by exposing their skin to ultraviolet B rays in sunlight, while some may take a supplement to boost their levels in winter.
But Tim Spector, Professor of Genetic Epidemiology, King’s College London, has become concerned that after promoting the supplements to patients with osteoporosis and other bone problems for decades, the vitamin may not be all it’s cracked up to be.
After researching his book, The Diet Myth, in 2013, Professor Spector, who used to take the vitamin himself and recommend it to friends and family through sun-starved winters, discovered a lack of evidence to support the health benefit claims of virtually all vitamin supplements on the market.
In an article in The Conversation, Professor Spector says, “Last year massive analyses combining 27 studies on half a million people concluded that taking vitamin and mineral supplements regularly failed to prevent cancer or heart disease. Not only are they a waste of money for the majority of us – but if taken in excessive quantities they can actually hasten an early death, increasing your risk of heart disease and cancer.”
In 2014, a British Medical Journal report found that our genetic makeup is actually what influences our vitamin D levels. And sometimes Vitamin D levels are naturally low in people, or become low because they already have another disease.
“While several studies in normal people failed to find any protective effects from vitamin D, others have been more worrying, says Professor Spector. “One 2015 randomised study of 409 elderly people in Finland suggested that vitamin D failed to offer any benefits compared to a placebo or exercise – and that fracture rates were, in fact, slightly higher [in those taking the supplement].”
Some people may have naturally high levels of Vitamin D in their blood because they spend lots of time outdoors, or because they are genetically built that way, which isn’t harmful at all, but trying to bring everyone up to one, specific, one-fits-all higher level of Vitamin D, when their levels are naturally lower, is what could be potentially harmful, according to the professor.
“Vitamin D mainly comes from UV sunlight converted slowly in our skin to increase blood levels or is slowly metabolised from our food,” says. “Any artificial addition of large amounts of chemicals will upset some sensitive immune processes.”
However, other scientists have disputed these claims and say research shows Vitamin D actually lowers the risk of heart disease, improves exercise performance and reduces production of the stress hormone cortisol, which in turn helps to prevent heart disease.
High levels of cortisol can raise blood pressure by restricting the arteries, narrowing blood vessels and stimulating the kidneys to retain water, so by reducing its production, Vitamin D may in fact lower the risk of cardiovascular disease.
Dr Emad Al-Dujaili produced a leading study into the vitamin’s effects at Queen Margaret University in Edinburgh which was presented to the Society of Endocrinology.
He found that adults supplementing their vitamin D had lower blood pressure compared to those given a placebo, as well as having lower levels of the stress hormone cortisol in their urine. A fitness test found that the group taking vitamin D could cycle 6.5km in 20 minutes, compared to just 5km at the start of the experiment. Despite cycling 30% further in the same time, the group taking vitamin D supplements also showed lower signs of physical exertion.
Dr Al-Dujaili says, “Vitamin D deficiency is a silent syndrome linked to insulin resistance, diabetes, rheumatoid arthritis, and a higher risk for certain cancers. Our study adds to the body of evidence showing the importance of tackling this widespread problem.”