Last year, Christopher Gardner, assistant professor of medicine at Stanford Prevention Research Center, wanted to see how garlic lowered bad cholesterol levels in blood. He had seen no conclusive proof of the herb’s efficacy during analyses of research literature. Yet, he did not doubt that it had some influence in lowering bad cholesterol, a belief that is now literally part of folklore. His study was thorough and lengthy. And at the end of six months, his conclusion was contrary to popular and even professional belief: garlic had no influence on lowering cholesterol levels. “We were stunned,” says Gardner, who published his results a few months ago.

In lab tests, garlic had been seen to reduce bad cholesterol. Likewise, animal tests have also showed that it has cholesterol-lowering properties. However, studies on humans had not been done widely enough. Most of the studies have been sponsored by companies who made garlic supplements. Gardner’s study was the most thorough independent study so far. His team studied garlic’s effect on 200 people who had high cholesterol. He also used widely well-known garlic supplements as well as raw garlic. “We found that none of them had any effect on lowering bad cholesterol,” he said.

Gardner had a top-notch team of experts consisting of biochemists, statisticians and statistical programmers. The study was very well funded too. Gardner is so convinced of his results that he says he would never again take a second look at garlic’s cholesterol-lowering properties.

So what does it mean to the millions of people who regularly take garlic and garlic-based supplements? Probably not much, if the aim is to specifically reduce bad cholesterol. Garlic provides many other health benefits. Even if it does not lower cholesterol, it might prevent cholesterol from causing heart disease. Or so we think.

Scientific attitudes towards health benefits of herbs and herbal supplements have of late been on a roller-coaster. Herbs thought to be good for health are now being questioned in some studies, while others that are proven to be useless are shown to be effective in certain other studies. Some herbs known to be good are being proven to be toxic in larger doses, while some others are being shown to be good only for certain individuals.

For example, tea is supposed to relax arteries and protect against heart disease. A few months ago, cardiologists and other scientists at the Charite Hospital in Berlin studied the effect of tea on arteries. What they found was surprising: tea was good, but without the milk. Tea contains a type of molecules called catechins that dilated blood vessels by producing nitric oxide. But in the presence of milk, which contains another substance called caesins, the amount of catechins reduced significantly. If we had taken this study to heart, we would have stopped adding milk to tea. But we need not.

Recently, scientists at the Rowett Research Institute and the Department of Environmental and Occupational Medicine, both in Scotland, found no such correlation. They found that the amount of catechins in tea was related to the amount of brewing and not milk. Both studies were published in peer-reviewed journals — the first in European Heart Journal and the second in the Journal of Agricultural Food Chemistry — within months of each other, but still seem to contradict each other.

What about herbs whose health benefits are supposed to be universal? Green tea, for example, has been known to be a virtual elixir for health. Yet, it can be harmful in larger doses. Green tea contains a substance called polyphenols, which protect against cancer and many other diseases. But Chung Yang of the New Jersey State University in Rutgers showed recently that polyphenols in large doses can also cause liver damage, a situation not uncommon if we take green-tea extracts. “I am not aware of any toxicity from drinking green tea, but there have been cases of liver damage when green tea extracts are taken as supplements,” says Yang.

Roger Thorneley at the John Innes Centre near Norwich, UK, recently found something even more alarming: drinking green tea in large amounts by pregnant women can cause birth defects in babies.

The combined message of all these studies: supplements may not work the way we think, and they are no substitute for a healthy diet and lifestyle.