Milk is said to be nature's nearly perfect food, so why the bad press? asks Claire O'Connell.
THE LACK of sunshine in Ireland is an annoying quirk of our climate.
And it also means that many of us risk running low on vitamin D, particularly in winter months. But fortifying milk with vitamin D could provide a ready answer to the problem, according to an expert who visited Dublin last week.
"Adding vitamin D to milk here seems to me to make very good sense," says Prof Robert Heaney of Creighton University in Nebraska, who was in Ireland last week on behalf of a brand of fortified milk on sale here to address nutritionists at a symposium.
Milk contains protein and calcium which, together with vitamin D, make a good package, explains Heaney, who researches bone biology.
"We all know calcium is important for bones.
"But if you don't have an adequate amount of protein in your diet, calcium does your bones no good, and that has not been generally recognised," he says.
"And if you don't have enough vitamin D in your body then the protein and the calcium together won't do your bones any good. So they all have to work together."
Vitamin D has been shown to reduce rickets, osteoporosis, cancer, tooth loss and hypertension, notes Heaney. One of its best-known roles is in regulating calcium absorption in the body, hence the link with bones, and it is also involved in switching on hundreds of genes within cells, he explains.
"Many of the tissues in our body do not have, in actual ready-to-go form, all of the molecular equipment they need to go with various stimuli. So they have to dip into their DNA library in order to get the plans to make the equipment that is needed to do a particular function.
"It turns out that vitamin D is the key that unlocks the DNA library. That's why you see so many effects."
We make vitamin D in our skins on exposure to sunlight, but covering up skin, using sunscreen or having poor-quality light in winter reduces the amount we can make.
The vitamin is present in only small quantities in a few foods such as oily fish and egg yolk, so getting enough in the diet can be a challenge without supplementation.
Unfortified milk from cows is low in vitamin D, explains Heaney. "Milk is accurately said to be nature's nearly perfect food, however the quantity of vitamin D it has is low, because a calf normally gets sun exposure so the calf doesn't need to get the vitamin D from the mother's milk," he says.
About 70 years ago, dairies in the US began adding vitamin D to milk, which addressed the problem of rickets in children, says Heaney.
"Putting it into food that's commonly consumed makes sense," he says. "If you are going to do something to improve general nutrition, the strategy is to use food that almost everybody eats."
And with the Irish being the second-highest consumers of milk in Europe, fortified milk is a good route to address public health issues, he believes. In addition, there's practically no risk of overdose, he adds.
"The best available evidence would suggest that a safe upper dose would be 10,000 international units, which is 250 micrograms, but we don't need that much and I can't imagine any medical situation where you might need to use it. So the number gives some idea of the margin of safety," he says.
"People are also sometimes afraid of getting too much vitamin D because they might absorb too much calcium, but in the absence of the body's need for calcium, vitamin D won't produce any calcium absorption, so it's quite safe.
"It's appropriate to have some concerns but let's not go overboard and throw the baby out with the bathwater."
He is also baffled by the bad press that milk sometimes gets. "I can't for the life of me figure out why. I think milk is an extraordinarily good product," he says, noting the results of the 20-year Coronary Artery Risk Development in Young Adults (Cardia) study, which monitored the lifestyles and health of thousands of people in the US.
"For the endpoints, insulin responsiveness, obesity, hypertension, the transition from health to disease was inversely proportional to dairy intake.
"The higher the dairy intake, the lower the risk. The transition from normal blood pressure to hypertension was reduced by up to 60 per cent in the high dairy consumers.
"The transition from overweight to obesity was down 30 per cent. There were still too many people becoming obese - dairy is surely not the answer to all the world's problems, but it's the answer to some of them."
And, contrary to popular belief, dairy products can help keep weight in check as part of a wider healthy lifestyle, says Heaney.
"The difference between a high milk consumer and a low milk consumer in a mature individual may be 10-15lb.
"If you are 400lbs, drinking milk isn't going to solve that problem, but an [ individual average] 10-15lb difference across the population has a tremendous impact on public health."
He welcomes that people in Ireland can buy vitamin-fortified milk, which has been available for more than a decade.
"To take this jump here in Ireland I think is a really giant step in the right direction. And I suspect a few years from now that you'll take another step and increase that level."