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Each year, about two million studies are published online or in a host of biomedical journals, some of them specializing in narrow branches of medicine, certain diseases or specific body parts. Even the experts don't know the exact number of journals - the estimate ranges from 10,000 to 20,000 worldwide.

However, the journals that contain clinical studies that might have some direct bearing on patient care can be narrowed down to about 160, according to Brian Haynes, chief of the health information research unit at McMaster University in Hamilton.

That's still a lot of journals, and they churn out about 60,000 studies a year. But just how good is the research?

Dr. Haynes estimates that only a small fraction of these studies - about 5 per cent - are both scientifically sound and potentially relevant to doctors and patients.

That doesn't mean most biomedical research is worthless, Dr. Haynes stressed. Science is an incremental process - two steps forward and one step back - and new findings, he said, must be confirmed by subsequent studies.

Nonetheless, a lot of studies seem to contradict each other, which certainly leads to confusion for the public and sometimes even for physicians.

Here is our wrap-up of this year's research highlights, including studies that were promising, disturbing or just plain dubious:

The big one

Possibly the most important medical study of the year dealt with research that was never published.

In January, a study in the prestigious New England Journal of Medicine provided the first hard evidence of a practice known as selective reporting, in which the good news about a drug is made public and the bad news isn't.

The study was led by Eric Turner of the Oregon Health & Science University in Portland. The researchers used the U.S. Freedom of Information Act to gain access to studies that pharmaceutical firms had filed with the U.S. Food and Drug Administration as part of the approval process for new antidepressant medications.

Dr. Turner and his team compared these formerly confidential antidepressant studies with what was eventually published in medical journals, which serve as a primary source of drug information for doctors. Their findings revealed that only the bullish antidepressant studies tended to see the light of day. The negative studies were essentially buried. As a result of this selective publication of favourable results, doctors and patients were left with a distorted picture of how well these drugs work. In other words, doctors could be prescribing drugs that aren't as effective as they thought or have under-reported side effects.

Another research team, led by Ida Sim of the University of California, San Francisco, embarked on a similar investigation of buried studies. Her team found that selective reporting is not just confined to antidepressant drugs but appears to be widespread throughout the pharmaceutical industry, according to their study published in October in the journal PLoS Medicine.

Dr. Sim and her colleagues argue that this practice amounts to "publication bias [that] harms the public good by impairing the ability of clinicians and patients to make informed decisions." They conclude: "Publication bias can thus be considered a form of scientific misconduct."

Scary stuff

A plastic compound known as bisphenol A became one of the leading health worries of 2008.

A growing body of research suggests the compound poses a potential threat because it can mimic estrogen. Experts fear it could lead to hormonal imbalances with a wide range of health implications.

BPA is an industrial chemical used to make epoxy resins and the hard, clear plastic known as polycarbonate. It has been used in lots of consumer products, including Nalgene bottles, once popular with hikers and campers. BPA is also in the epoxy lining of almost all canned foods.

The amount leaching from cans and plastic bottles is infinitesimal - only a few parts per billion - but it's still many times higher than the level of natural estrogen circulating in the body.

In October, the federal government decided to add bisphenol A to its list of toxic substances - making Canada the first country to take such decisive action against BPA. The move gives Ottawa the authority to limit human exposure to the substance. Federal officials focused their attention on infants, who might be less able than adults to remove the substance from their bodies. The main worry is that infants could be getting too much of the chemical from canned baby formula and plastic feeding bottles. The federal government has proposed banning BPA from baby bottles to minimize exposure for children under 18 months.

Even so, public health and environmental advocates say Ottawa hasn't gone far enough and should be protecting people of all ages. Some scientists think BPA may play a role in health trends linked to sex-hormone imbalances, such as earlier puberty in girls as well as prostate and breast cancers.

Furthermore, a study published in the Journal of the American Medical Association in September found that adults with higher exposures to BPA had 2.9 times the odds of developing cardiovascular disease and 2.4 times the odds of getting adult-onset diabetes, compared with those with lower exposures.

Another study, published in the Proceedings of the National Academy of Sciences, suggests BPAmight alter brain function and contribute to neurological ailments such as depression, Alzheimer's disease and schizophrenia.

Nalgene, meanwhile, has reformulated its bottles so they no longer contain BPA, and other companies are following suit. But it's still in many products - especially canned foods.

The sunshine vitamin Vitamin D is emerging as the superstar in the supplement sector.

Indeed, there were many disappointing studies involving other vitamins. Trials failed to show that antioxidant supplements such as C, E and B vitamins (folic acid, B6 and B12) could halt heart disease. And a study of vitamin E and selenium indicated these supplements don't prevent prostate cancer - and they may actually increase the risk of the disease.

But it has been mostly good news for vitamin D, the "sunshine vitamin," which is made naturally in human skin exposed to sunlight. Years ago, it was thought that vitamin D was mainly good for preventing rickets, a bone deformity in children. Numerous studies published this year and earlier have helped bolster hopes that vitamin D might also guard against certain cancers, multiple sclerosis, heart disease, depression and other illnesses.

One sour note was sounded by a vitamin D study published in the U.S.-based Journal of the National Cancer Institute. It found that vitamin D supplements had no effect on the risk of developing breast cancer. But women in the trial were taking only 400 international units of D a day - well below what some experts consider to be a therapeutic dose.

For instance, the Canadian Cancer Society recommends that Caucasian adults pop 1,000 IUs a day during winter and fall, when the sun's rays are too weak to produce vitamin D in the skin. The cancer society says those over the age of 50 and non-whites should be supplementing at that rate year-round.

Experts at the World Health Organization think there is now enough promising preliminary research to justify conducting an expensive, large-scale, drug-style clinical trial to properly evaluate the vitamin's cancer-fighting potential.

Dopey study?

If an award were handed out for the most questionable research of the year, a leading contender would be a marijuana study by researchers at the U.S. National Institute on Drug Abuse.

According to the findings published in the journal Molecular Psychiatry, smoking marijuana may boost your chances of having a heart attack or stroke.

The researchers found elevated levels of a specific protein called apolipoprotein C-III in the bloodstream of heavy users of marijuana. This protein, in turn, leads to increased levels of triglycerides, fats that can clog arteries and increase the risks of heart disease and strokes.

But you apparently have to smoke an awful lot of dope. The 18 marijuana users who volunteered for the study smoked from 78 to 350 joints a week. The average was 130.

The researchers couldn't say, without doing another study, whether moderate and occasional smokers of weed have elevated levels of the protein.

Marijuana activists said the high levels of pot used in the study render the results meaningless.

"If you do anything to that level of excess, it might well have some untoward effects, whether it's marijuana or wine or broccoli," Bruce Mirken of the Marijuana Policy Project told Reuters.

Trendsetters

Research into the benefits of hallucinogenic drugs may be coming back into vogue after being shunned by mainstream scientists for decades.

A small but growing number of scientists in the United States and Europe are again recruiting patients for studies of the controversial drugs, such as psilocybin, LSD and DMT.

And in July, a team of researchers at Johns Hopkins University in Baltimore released the follow-up results of a study involving 36 volunteers who were given psilocybin - the chemical ingredient in "sacred" or "magic" mushrooms - in a carefully controlled laboratory setting.

A questionnaire completed 14 months after the one-day drug trial found the majority of participants considered the experience to be one of the most "personally meaningful and spiritually significant" events of their lives. Even more surprising, they felt the drug had a long-lasting effect that significantly contributed to their overall sense of well-being and life satisfaction.

Matthew Johnson, one of the authors of the study published in the Journal of Psychopharmacology, said the mind-altering aspects of hallucinogens could help cancer patients come to terms with their impending death. The drugs might also assist people overcoming certain addictions through greater self-awareness.

Still, there is a risk the drugs could trigger anxiety and paranoia - basically "a bad trip" - and precautions need to be taken to safeguard study participants and prevent the excesses of the psychedelic 1960s, which tarnished legitimate research in the field.