Smoking appears to be more harmful to the arteries of whites than to Chinese, according to a study in the 1 September issue of the Annals of Internal Medicine. The next step is to identify the protective factor or factors, and that could lead to new ways of minimizing smoke-related blood vessel damage, the authors say.

The research was inspired by the fact that, although 70% of Chinese males smoke, coronary artery disease is only 20% as prevalent in southern China as it is in the West. Smoking damages the endothelial cells that line arteries, and helps bring on heart disease by inhibiting arteries' ability to dilate. So Kam Woo of the Prince of Wales Hospital in Hong Kong and colleagues decided to see if Chinese and white arteries actually react differently to smoking.

The subjects were 144 healthy young adult subjects, half Chinese and half British or Australian, who were either smokers (with histories averaging out to a pack-a-day habit for about 8 years); nonsmokers; or "passive" smokers. The researchers tested arterial dilation on the brachial artery in the arm, using ultrasound to measure the "flow increase" that occurs after a blood pressure cuff is released.

Blood vessel dilation in non-smokers was the same--about 8%--regardless of ethnic group. But smokers differed dramatically: Smoking seemed to have no effect on the vessels of the Chinese, while in whites dilation decreased by about two-thirds. The race difference also appeared in passive smokers.

Woo and colleagues note that the Chinese advantage shows despite the fact that many Chinese smoke locally made cigarettes that are higher in tar and nicotine than those smoked by white subjects. But they suggest that the Chinese may be benefiting from antioxidant-containing teas and high intake of foods such as soy protein and fish oil.

The diet difference is certainly "the simplest explanation," says cardiologist William Parmley of the University of California, San Francisco. But genes are also a possibility, says population geneticist Mark Shriver of the Allegheny University of the Health Sciences in Pittsburgh, who observes that the only way to find out what's protecting the Chinese would be a study of a thoroughly acculturated migrant population.