Rachel Jennings is one of millions of women who have invested heavily in protecting their children from the perils of skin cancer.

For years she has taken care to limit their exposure to the sun during the hottest periods of the day; for family holidays to sunny destinations she has always gone weighed down with the latest sunblocks.

Now she is dismayed to discover that while protecting her children from sunburn and skin cancer, she might have also inadvertently put them at risk of other cancers, heart disease and further illnesses by depriving them of sunlight.

This is because the sun’s ultraviolet radiation is our main source of vitamin D — and scientists now believe that vitamin D deficiency is closely linked to a range of cancers and other diseases.

This week an American analysis of 63 studies published over the past four decades concluded that cancer tumours of the colon and breast are linked to low levels of vitamin D. Other studies have found a link between vitamin D deficiency and schizophrenia, multiple sclerosis and lung diseases.

“It really is impossible to know what to do,” said Jennings, 38, who has two sons: Joe, 9, and Charlie, 6. “I don’t necessarily believe that I have increased their risk of all these horrible things, but it is impossible not to worry as a mother.”

Like many other consumers Jennings is baffled: the more health advice that we receive, the more confusing, if not downright contradictory, it can seem.

In the past few months, for example, scientific journals have reported that coffee might cause fatal heart disease — and that it is full of cancer-preventing antioxidants.

Milk, which contains calcium, is good for the bones — but its fat is bad for the arteries. Red meat is bad for the heart — but high-protein diets, claim some, can help to avoid obesity. A high-fibre diet is good — except that an American study now says that it does not, after all, prevent cancers of the digestive system.

Within days of each other last month, one study was published claiming that an aspirin a day reduced heart disease in women by 25% — but another said that one in 10 of those who take aspirin is at risk of intestinal bleeding and a possible early death.

Science is complex and good health involves balancing one risk against another. But for ordinary consumers, sifting the plethora of different advice is becoming an ever more complex task.

“When you see these headlines you can’t help wondering if we should be looking for the vested interests behind all health advice,” said Jennings, a former marketing executive who now works part-time near her home in Hersham, Surrey. “Have we been peddled the scare about skin cancer by a cosmetics industry that just wants to sell more sunblock, and the vitamin D message by the dietary supplement manufacturers who want to sell more pills?

“The trouble is, it is impossible not to be influenced by it.”

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