As new research claims that Vitamin D can reduce blood pressure, experts talk about the many wonders of the 'sunshine vitamin' and discuss whether sun-starved Brits could benefit from vitamin D supplements.
By Lisa Salmon.
Its power to strengthen bones and muscles has been well known for years. But now there's increasing evidence that this vitamin D may exert a positive influence over many other parts of the body.
New Danish research has confirmed that vitamin D - known as the 'sunshine vitamin' because 90% of it is made in the skin when it's exposed to sunlight - can help lower blood pressure.
The study on 112 patients at the Holstebro Hospital in Denmark found that taking a vitamin D supplement led to a "significant reduction" in blood pressure.
And just last week, a study by the Medical Research Council's (MRC) lifecourse epidemiology unit found that the children of women who were deficient in vitamin D during pregnancy were fatter as they grew older than children born to women who weren't vitamin D deficient.
The studies add to a growing body of research which suggests vitamin D may keep the immune system healthy, and reduces the risk of some cancers, while being deficient in the vitamin may increase the risk of chronic health conditions such as multiple sclerosis, diabetes and cardiovascular disease.
The MRC's lifecourse epidemiology unit's director, Professor Cyrus Cooper, says that in the last 10 years there's been an increasing amount of research into vitamin D and health problems such as diabetes, obesity, blood pressure, heart disease, auto-immunity and multiple sclerosis.
"There's been a lot linking vitamin D in observational data with all those outcomes," he says.
"They're interesting, because the vitamin D receptor is found on lots of different cell types, including cells of the immune system, the vascular system and smooth muscle, so it's conceivable that it has cardiovascular, immune and other effects."
However, he stresses that these effects need to be "demonstrated rigorously" in clinical trials.
In the meantime, Cooper says people should be aware of how to get vitamin D - mainly from exposure to UVB rays from sunlight in the summer months and, to a much lesser extent, eating oily fish.
Currently, the Department of Health estimates up to a quarter of the population has low levels of vitamin D. This is thought to be because people are spending less time outdoors; sunscreen is often applied when it's sunny, preventing the synthesis of vitamin D in the skin, and more people are keeping their skin covered for cultural reasons.
You're unlikely to know you have low vitamin D levels without having a blood test, as the effects tend to become apparent over the longer term. As well as the health implications currently being researched, like multiple sclerosis, high blood pressure and obesity, it's known that vitamin D ensures people absorb enough calcium to keep bones and teeth healthy, so low levels can lead to brittle bones and osteoporosis.
Rickets risk Children with low levels of vitamin D are also at risk of the bone-weakening disease rickets, known for causing bow legs. They can even be born with the condition if their mother has vitamin D deficiency during pregnancy, and this was highlighted in December when the parents of four-month-old Jayden Wray were cleared of his murder after it emerged at their trial that the baby's numerous fractures, including the head injury that killed him, were likely to have been caused by undiagnosed rickets.
Baby Jayden is thought to have been born with the condition, which was eradicated in the UK in Victorian times but is now on the increase again, because his mother had an undiagnosed vitamin D deficiency.
Tragic cases like Jayden's illustrate why the Department of Health currently recommends that people in groups at risk of vitamin D deficiency, including pregnant women, take a daily vitamin D supplement. Earlier this year, the UK's four Chief Medical Officers wrote to health professionals reminding them about vitamin D deficiency and the recommendations.
At risk As well as pregnant women, those at risk of vitamin D deficiency include breastfeeding women, children under five years, the over-65s, those who have low or no exposure to the sun, like people who cover their skin for cultural reasons, who are housebound or do night shifts, and people who have darker skin, such as those of African and South Asian origin, because their bodies can't make as much vitamin D.
Official advice currently only recommends that those at risk take vitamin D supplements, although the independent Scientific Advisory Committee on Nutrition is currently reviewing the recommendations. However, the results aren't expected until 2014.
But registered dietician Dr Carrie Ruxton, spokesperson for the Health Supplements Information Service, warns: "Now we're all indoors at our computers, the kids are indoors, and gradually we're all eating away at our ability to make vitamin D naturally."
UK weather problems Cloudy skies mean the skin produces less vitamin D, and for this reason in the UK people usually only make it over the summer months, from about the end of April until October, and between around 10am and 3pm.
Pollution, sunscreen and clothes also reduce the amount of vitamin D produced.
The vitamin can be stored in the body for up to three months, and ideally people make enough over the summer to get them through the winter.
Dr Ruxton says: "It used to work in the old days that you got a good blast of vitamin D in the summer and had a bit of oily fish in the winter to keep it topped up until you started making it again around April. It's a bit like recharging a battery.
"But now because we're not fully topped up at the end of summer and not eating as much oily fish, people get depleted around December."
She says that "the jury's still out" on how much vitamin D is needed in the blood, but says 10mcg a day is recommended for people in the at-risk groups, with the exception of babies and young children who should get 7mcg daily.
"We're now at the stage where for things like heart health and immune function, we don't have the evidence to say how much vitamin D is needed," says Dr Ruxton.
"To cut through the confusion, we can say there's some interesting research that's taking vitamin D in a different direction, and it may be in the future we need to have more.
"But at the moment if we stay with the recommended 5-10mcg a day, and whether you want to take a supplement, or eat more oily fish and get out in the sun more, it's up to you - there's different ways of getting it.
"But if you don't get outside enough and you don't eat oily fish, take a supplement. And if you're in an at-risk group, take a supplement anyway."
Careful sunshine The best way of all to increase vitamin D levels is to get out in the sun. However, over-exposure to the sun can, of course, lead to skin damage and cancer.
Deborah Mason, spokesperson for the British Association of Dermatologists, warns that excessive sun exposure is the main cause of skin cancer.
But she says: "Enjoying the sun safely, while taking care not to burn, can help to provide the benefits of vitamin D without unduly raising the risk of skin cancer.
"The time required to make sufficient vitamin D is typically short and less than the amount of time needed for skin to redden and burn. Regularly going outside for a matter of minutes around the middle of the day without sunscreen should be enough."
She says people should get to know their own skin to understand how long they can spend outside without risking sunburn, and adds: "When it comes to sun exposure, little and often is best, and the more skin that's exposed, the greater the chance of making sufficient vitamin D before burning."
:: Do you get enough Vitamin D?
Dr Carrie Ruxton advises everyone to ask themselves: :: Do you get outside regularly - for around 15 minutes a day in the summer?
:: Are your face, arms and/or legs exposed to the sun when you go outside?
:: Do you eat a diet rich in vitamin D, including oily fish (eg salmon, sardines, trout) at least once a week? Smaller amounts of vitamin D are also found in eggs and meat, and it's added to margarine, some breakfast cereals and infant formula.
:: If you don't get enough vitamin D from natural sources, do you take a supplement?