The group of vitamins known as vitamin D are crucial for good bone health in humans. In particular, the compounds vitamin D2 and vitamin D3 are important for regulating the amount of nutrients such as calcium, phosphate and magnesium in the body.
During the summer months, the body is able to create vitamin D from the UV light coming from the Sun. But from October to March, the NHS recommends we have an additional source of the vitamin, be it foods high in vitamin D – such as oily fish and red meat – or by taking dietary supplements.
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Previous studies have suggested there is a link between low levels of vitamin D and a higher risk of depression in later life, but until now, no large-scale trial has investigated the association.
Researchers from universities and hospitals in America observed over 18,000 adults aged 50 or older to see if taking vitamin D daily for an average of five years would help prevent them developing depression.
Half of the participants took a vitamin D3 supplement, while the others took a placebo. Neither the participants nor the researchers knew who received which treatment, in what is called a double-blind study.
None of the 18,353 men and women involved in the study had depression, or depressive symptoms, at the start of the research. Throughout the study, they were asked to complete questionnaires, attend in-person psychiatric diagnostic interviews, and report any diagnosis of depression or prescription of treatment for depression.
After five years, researchers saw no significant differences between those taking the supplement and those having a daily placebo
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"There was no significant benefit from the supplement for this purpose. It did not prevent depression or improve mood," said lead author Dr Olivia I. Okereke, from Massachusetts General Hospital.
That’s not to say that vitamin D does not have other health benefits.
"Vitamin D is known to be essential for bone and metabolic health,” said the paper's senior author, Dr JoAnn Manson, at Brigham and Women's Hospital.
"It's not time to throw out your vitamin D yet though, at least not without your doctor's advice," said Okereke.
Reader Q&A: Can you absorb vitamin D through a window?
Asked by:Steven Collins, by E-mail
You don’t absorb vitamin D from the Sun, your skin synthesises it in response to sunlight. It’s the UVB portion of the ultra-violet spectrum that’s needed.
Ordinary window glass is only transparent to wavelengths of light longer than 330 nanometres. But to synthesise vitamin D, we need UVB wavelengths between 270 and 300nm. You can get a suntan through glass, but to make vitamin D you need to be outside. On the other hand, at least 50 per cent of UVA can penetrate through glass, so skin ageing can still take place.
So, you can become deficient in vitamin D if you don’t go out and don’t eat enough oily fish or dairy products to compensate.
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