Caffeine dependence is all in the genes

Shelley Page, The Ottawa Citizen Published: Monday, June 11, 2007

A University of Toronto study has shown that there is a genetic basis for caffeine-seeking behaviour.

While stopping short of calling it "caffeine addiction," researcher Ahmed El-Sohemy said men who possess certain dopamine-receptor genes experience an elevated mood after consuming a caffeinated beverage.

The study was based on 600 students from the University of Toronto who were asked to document their reactions to caffeine and provide samples of their blood.

Men who experience this elevated mood seek out caffeine to continue to feel elation. Those who don't report elevation of mood might be less vulnerable to caffeine dependence, Mr. El-Sohemy said.

The same genetic link has so far not been found in women.

Mr. El-Sohemy, a nutritional sciences professor who holds the Canadian Research Chair in Nutrigenomics, said the gender differences were puzzling and require more investigation, but are not entirely surprising. It might be linked to the differences in how women process dopamine compared to men. It is also well known that women metabolize caffeine at a much slower rate than men.

The 600 subjects were asked to rate how they felt within 12 hours of consuming caffeine. Mr. El-Sohemy wanted to know whether subjects felt an elevation of mood and increased energy. He also wanted to know whether, after 48 hours without consuming caffeine, the subject experienced headaches and nausea and felt irritable.

The blood samples were also analysed to look for certain genes related to dopamine, a chemical in the brain known to affect mood.

Mr. El-Sohemy found that 22 per cent of men with a particular form of the dopamine receptor gene experienced an elevated mood after consuming a caffeinated beverage.

More than 60 per cent of men with a different form of this gene reported the same kind of mood elevation, which Mr. El-Sohemy described as a "fairly big effect." He still has to figure out what other factors influence whether or not men experience an elevated mood.

Fifty per cent of women who consumed caffeine reported experiencing an elevated mood after consuming caffeine, regardless of the version of the gene they possessed. The research was funded by Canada's national Advanced Foods and Materials Network.

Mr. El-Sohemy said there has been an ongoing scientific debate as to whether there is a biological basis for caffeine-seeking behaviours. The World Health Organization recognizes that people can be dependent on caffeine, whereas the DSM-IV, the Diagnostic and Statistical Manual of Mental Disorders, does not.

These results may provide a genetic explanation as to why some people become dependent on caffeine and others do not.

(Flickr photo : Starbucks addict)