Every once in a while, some unsung nutrient gets rediscovered and, in the course of a few short years, is rendered virtually magical in the eyes of health professionals and consumers. Foods containing the nutrient come into vogue and supplement use soars.
Then, seemingly overnight, the spell is broken.
Last week, it was vitamin D's turn to fall from grace.
The comedown came courtesy of an expert panel convened by the Institute of Medicine, which advises the government on health issues. The panel's exhaustive report concluded that levels of vitamin D are — thank you very much — just fine in virtually all healthy North Americans.
That was surprising to the legions of people who believed that high doses of the vitamin could prevent a laundry list of chronic conditions, including type 2 diabetes, cardiovascular disease, depression, certain cancers, preeclampsia and low birth weight. Their faith in vitamin D, derived from a heap of preliminary studies, prompted many to take mega-doses of the nutrient daily.
But the expert panel was unconvinced. It noted that the scientific evidence has been mixed. Moreover, it worried about the risk of undesirable side effects, such as kidney stones, that might come with high levels of supplementation.
In short, the jury's still out on the benefits of vitamin D beyond its traditional role in promoting the absorption of calcium for healthy bones. To do that job, virtually all healthy people need only 600 international units (IUs) of vitamin D a day — and those older than 70, 800 IUs.
More does not make your bones healthier.
So, after all the hype and hope surrounding vitamin D, what's a consumer to do now?
Here's a look at what the expert panel said, and why it reached its controversial conclusions.
How much vitamin D did the experts say is necessary?
For most children, teens and adults, a daily dose of 400 international units (IUs) of the vitamin is sufficient, and 600 IUs recommended. Seniors older than 70 should ideally receive 800 IUs of vitamin D a day, the panel determined. For babies less than 1 year old, the panel considered 400 IUs of vitamin D enough.
Those levels are somewhat higher than the ones set in 1997, the last time a government panel examined vitamin D intake. But they are far below what many doctors and supplement advocates had been urging.
Why weren't they higher?
The idea that people could benefit from daily doses as high as 2,000 IUs is based on the belief that vitamin D can reduce the risk of many chronic diseases, including type 2 diabetes, cardiovascular disease, metabolic disturbances, depression and certain cancers.
A slew of recent studies have linked low levels of vitamin D to an increased incidence of these health problems. But the expert panel concluded that the studies were not convincing — many, in fact, showed no such connection — so it based its recommendations only on the amount of vitamin D needed to maintain bone health and prevent fractures.
Does that mean I should give up my vitamin D supplements?
Maintaining a healthy level of vitamin D through diet alone has become much easier since manufacturers began fortifying foods with the nutrient. Fortified foods — including virtually all milk, many brands of orange juice, and some cheeses, yogurts, margarines and breakfast cereals — are now some of the richest dietary sources of vitamin D. High levels exist naturally in fatty fish such as tuna, salmon and mackerel, and it's also present in egg yolks and beef liver.
But there are a lot of people who may still need to add a vitamin D pill to their daily diet. For instance, people who follow a vegan diet need to look hard for supplemental sources of Vitamin D, as do those with milk allergies, lactose intolerance, and people who rarely eat fish.
"We didn't actually say in the report that supplementation is verboten," said Dr. Glenville Jones, an endocrinologist at the University of Queensland in Canada who was on the expert panel.
So I should keep on buying foods fortified with vitamin D?
Definitely, says Katherine Tallmadge, a registered nutritionist and spokeswoman for the American Dietetic Assn., which endorsed the panel's report. In fact, the fortification of foods probably contributed significantly to the panel's finding that most North Americans get enough of the nutrient, even as they raised the recommended daily levels.
Can't I get some of the vitamin D I need from the sun?
Indeed, the sun is a free, plentiful source of vitamin D. When the sun shines on human skin for at least five to 15 minutes, the body produces the nutrient. But with people spending more time indoors and using sunscreen to prevent skin cancer, this source has fallen on hard times. In fact, the panel didn't even factor in vitamin D from sun exposure when it made its recommendations.
Does that mean I should lay off the sunscreen?