Tackling the coffee conundrum
You could get whiplash trying to keep up with news about the health effects of this or that vitamin or food product. Some researchers say genetics holds the key to saving epidemiology from its flip-flops
Oct 13, 2007 04:30 AM
Here's a pop quiz for nutrition buffs: Does folic acid keep prostate cancer at bay? Can vitamin E stop heart disease in its tracks?
Epidemiological studies – which follow the habits that contribute to health or lead to illness within populations – routinely make headlines. But often it isn't long before another study, and another headline, comes along contradicting the first.
At one time researchers thought vitamin E protected people from cardiovascular disease and beta-carotene shielded men and women from a whole slew of cancers. But the fervour didn't last long. Follow-up studies showed that adults taking beta-carotene supplements had an increased risk of lung cancer, and the effects of vitamin E seemed exaggerated.
When it comes to health and disease, there's considerable confusion over which nutrients and vitamins will give you an edge.
"For the researchers each study brings a piece of the puzzle, but to the public it looks like we're flip-flopping," says France Gagnon, Canada Research Chair in Genetic Epidemiology at the University of Toronto.
Some critics say that more than half of all epidemiological studies are incorrect or misleading, and that these poor studies have damaged epidemiology's reputation. Can genetics help salvage this science?
Epidemiology has a rich history of successes. The science uncovered the causes of cholera and lung cancer, but has had much more difficulty picking apart more subtle health questions, including the relationship between nutrients, health and disease.
Two epidemiological studies published in the early 1990s suggested that vitamin E protected people from heart disease. Both were cohort studies – studies that follow a group of people over time and look at how many of them are newly diagnosed with the disease. One followed more than 87,000 middle-aged female nurses for up to eight years. The other followed 40,000 male health professionals for four years. None of the participants in either group had heart disease when they enrolled in the study. At the end of the studies, the data showed promising results – vitamin E supplements appeared to be associated with 20 to 40 per cent fewer cases of heart disease.
But when researchers at the Hamilton General Hospital put vitamin E to the test in 2000, it failed. They enrolled more than 2,500 women and nearly 7,000 men with a high risk of cardiovascular disease into a randomized controlled trial. Treatment with vitamin E changed little for those with a high risk of heart disease.
Back-and-forths like this have left health-conscious individuals and doctors in a tizzy. In some cases, the associations between health and disease were communicated to the public too early. "In many cases we have pulled the trigger before we should have," says Jose Ordovas, a molecular biologist at Tufts University in Boston. "You cannot bring the bullet back."
"We really need these studies to be repeated numerous times and getting a result that is fairly consistent before we jump on the bandwagon and say this is what we should be doing," says Katherine Gray-Donald, an epidemiologist at McGill University.
Others argue that observational studies and randomized controlled trials ended up asking different questions.
Vitamin E's fate may not yet be sealed. The earlier observational studies followed people without heart disease, whereas the later randomized trials looked at people with a known risk for heart disease.
Coffee has also had its fair share of ups and downs. Observational studies have found that moderate consumption – a few cups a day – has been associated with lower risk of developing Type 2 diabetes and colon cancer.
Some epidemiological studies have found that coffee drinkers have a greater risk of heart attacks, whereas others have suggested that it can protect against heart attacks.
To clear away some of the clutter, Ahmed El-Sohemy, Canada Research Chair in Nutrigenomics and an assistant professor of nutritional sciences at the University of Toronto, used genetics to understand whether coffee and heart attacks went hand-in-hand.
El-Sohemy focused his work on the machinery that breaks down caffeine. The enzyme is much less active in some people than in others, a trait that is associated with a one-letter change in their genetic code. He found that only the slow caffeine metabolizers had an increased risk of non-fatal heart attacks.
Although the study isn't the last word on coffee and health, the genetic approach encouraged by El-Sohemy and others addresses a long-standing issue in nutrition and epidemiology: How much of the nutrient is actually available in the body to have an effect.
"Genetics can give us a more accurate measure of exposure," says El-Sohemy. "You take into account individual differences and how that nutrient is metabolized."
Before this genetically influenced advice can make it into the clinic, more studies need to be done. Interesting interactions seen in the field have to be tested in randomized controlled trials. This means selecting people with different genetic patterns of interest, putting them on different diets and observing the response.
"What we have now are small holes in the wall. We need to start converting those holes to windows," says Ordovas.
"Genetics can provide meaningful information and epidemiology can provide meaningful information. We can get at some of the answers by merging the two." But there is also the bigger public health picture to consider. "We have a huge amount to do to help the population eat well," says Gray-Donald. "There are huge nutritional problems that could be solved without spending our finite resources on things that will be very, very costly, like looking at someone's genetic makeup to see if they need a little bit more or less of this or that."
"In terms of public health – for the general population – we know the answer already: If people were compliant with the current dietary recommendations, they would be in quite good shape," says Ordovas.