As Britain basks in the sunshine, who'd be the parent caught short in the park this week without that essential must-have, a bottle of factor 40? Gone are the days when the arrival of summer meant that children stripped off and raced out of doors: today's youngsters venture outside in the heat of the sun only when kitted out in top-to-toe UV-safe sunsuit, protective goggles and tie-on legionnaire-style hat.
But getting wise to the dangers of sunshine, it seems, may come at a price: and that price, according to Dr Michael Holick, professor of dermatology at the Boston University School of Medicine, is that we are missing out on essential vitamin D. Fine to cover up so we don't get burned: not so fine in shielding ourselves - and our children - from the goodness, as well as the badness, of the sun. As much as 95% of the vitamin D in our bodies comes from our exposure to sunlight, says Holick - and if we don't get enough we are risking other health problems.
Cancer charities, which have been bombarding us for more than 15 years with the message that covering up and slapping on the sunscreen is the way to behave in the sun, have greeted Holick's comments with dismay: the last thing a public health campaign needs, they say, is to confuse the public about what is and isn't the responsible way to behave. But could Holick be on to something? Could we be jeopardising our long-term health by over-reaction?
Sara Stanner, senior nutrition scientist at the British Nutrition Foundation, says many nutritionists were shocked when the government's national diet and nutrition survey in 2000 showed poor vitamin D levels in some children. Shock-horror headlines foretold the return of rickets, since the main benefit of vitamin D is to help the human body absorb calcium, and so aid the growth of healthy bones. But the fact that rickets is unlikely to make a reappearance in the UK in any significant proportion does not detract, says Stanner, from the fact that there is a genuine concern. "Sunlight is the main source of vitamin D - it's possible to find it in meat and fish and dairy products, but these are the foods we're often trying to cut down on and for children it's very difficult to get enough of the vitamin through food intake.
"What all the research shows is that the early years are crucial in building up healthy bones. Most people reach peak bone mass in their teens and early 20s, and we know that from that peak, bone density always declines. So what we're talking about is a decline from a high bone density, or a decline from a lower bone density - and obviously you're going to have healthier bones in your later years if you've had high density in your youth."
Stanner admits that the nutritional message about a need for exposure to sunlight sits uneasily alongside research linking melanoma in later life with just one bad bout of childhood sunburn. The answer, she believes, is to encourage parents to allow children short bursts of sun screen-free play out of doors, at a time of day when the sun is shining, but UVB rays - the burners - are weakest.
Sara Hiom of Cancer Research UK's SunSmart campaign, says, "The sun's rays are at their strongest between 11am and 3pm, peaking at 1pm. Around 90 or 95% of the sun's rays are concentrated in this period - but outside it, even if the sun is shining, you're only getting around 10% of the sun's rays."
But vitamin D isn't the only nutrient we're missing out on because of current wider health concerns. Iron deficiency, especially in children, is of increasing concern to nutritionists - and although doctors aren't yet entirely clear about its long-term implications, they do believe there's enough evidence to suggest we should be a lot more worried than we are about the fact that too many youngsters are getting too little iron.
According to Professor Stuart Logan, a paediatrician at the Peninsula Medical School in Exeter, a "substantial proportion" of UK toddlers are currently iron-deficient, according to World Health Organisation guidelines. The problem, in a nutshell, is dietary: we have stopped giving our children enough red meat, partly because we have heard the message about red meat containing too much saturated fat and have failed to clock that what matters for adults isn't always what matters for children.
Stanner says she was "horrified" to discover recently, when assessing nutritional standards in nurseries, that many offer it as a boast to parents that their menus "contain no red meat". But red meat is exactly what small children should be eating, she says. "We recommend red meat as an ideal weaning food. The whole idea of weaning a baby at six months is because, especially when they're breast-fed, their iron reserves are low and they need a boost. And red meat is the most easily available form of iron - you hear people saying green leafy vegetables contain lots of iron, and they do, but the point is our bodies don't absorb it as easily as they do from meat."
According to Logan, the jury is out on how serious a problem this is. "There was a trial in Indonesia that suggested that IQ levels could be significantly improved if children with a mild iron deficiency had their levels improved," he says. "Other studies haven't always backed this up, but we urgently need to do more research. If increasing iron levels in children could make a difference to their intelligence levels, we should be increasing them."
Other fads and elements of our 21st century western diet are leading to other deficiencies, too - and as with iron, there are still questions to be answered on how far-reaching the implications could be. Midwife and author Zita West says she has long been concerned at falling levels of zinc in the human body: one of her big concerns is infertility, and she believes the two are related.
"Zinc deficiency is one of the most common nutritional problems I come across," she says. "It's needed for growth and cell division in the foetus, and for enzymes to work. Semen is rich in zinc, and research shows that a male foetus needs five times as much zinc for its development than a female foetus. And as zinc is closely connected with our hormone system, I think that could explain why post-natal depression is more common after the birth of a boy than a girl. The placenta is also rich in zinc, which is one of the reasons why, in a lot of animal species, the female eats the placenta after giving birth."
Good food sources for zinc include meat, fish, eggs, grains and pulses - but West believes that it's not just a reduction in the sorts of food we're eating, but also that industrial farming methods have depleted the levels of zinc in the soil, that have contributed to the problem.
Like zinc, a deficiency of selenium has been linked with reproductive problems - but, according to Stanner, changes in the pattern of wheat importation into the UK mean increasing numbers of us are not taking enough of the mineral into our bodies. "We used to get our wheat from the US and Canada, where the soil is rich in selenium so we were eating the recommended levels. But now most of our wheat comes from Europe, and it's got much lower selenium levels. Shellfish is a rich source of selenium, so it may be that in some other European countries the low levels of selenium in wheat wasn't a problem as the population tended to eat more shellfish.
"The health implications are being debated at the moment," continues Stanner, "and it's not clear how serious they are. But there are some indications that selenium could protect against coronary heart disease and some forms of cancer, so it's certainly something we should be taking seriously and looking into."
