Whether a person starts smoking and how many cigarettes they smoke a day may be largely determined by their genes, according to a new study.

Researchers found that having family members that smoke not only increases the chance that young people will start smoking cigarettes, but it also influences how many cigarettes they smoke per day and how addicted they become to nicotine.

The large study of Dutch twins suggests that a combination of shared genetics and environmental factors plays a major role in determining a person’s cigarette smoking habits.

But researchers say having a genetic predisposition for nicotine addiction doesn’t mean that someone will become addicted to tobacco or unable to quit. They say smokers with a genetic predisposition can still quit smoking, but they may find it harder to quit smoking than others.

The news comes as millions of Americans are trying to quit smoking for at least one day as a part of today's annual Great American Smokeout, sponsored by the American Cancer Society.

Hard to Quit Smoking? Blame Your Genes

In the study, published in The Pharmacogenomics Journal, researchers looked into the link between genetics and smoking habits of 3,657 Dutch twin pairs. About half of the twins had never smoked.

They found both smoking initiation and number of cigarettes smoked per day were strongly influenced by environmental and genetic factors.

For example, the study showed genetic factors explained 36 percent of the variability in whether twins started smoking or not. Shared environmental factors, such as exposure to smokers at school or in the neighborhood, explained 56 percent.

In addition, researchers found shared genetic factors explained 51percent of the differences in how many cigarettes the participants smoked, while shared environmental factors explained 30 percent of this difference.

Researchers say genes located on chromosomes 6 and 14 appear to be involved in whether or not a person starts smoking, and a region on chromosome 3 affects how many cigarettes are smoked a day.

But they say further research is needed to confirm these results as well as determine whether genes might help explain why some people have a harder time quitting smoking than others.

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Vink, J. The Pharmacogenomics Journal; vol 4: pp 274-282. News release, Netherlands Organization for Scientific Research. News release, American Cancer Society.