Less then five cigarettes a day almost triples a person's risk of dying of heart disease, according to Norwegian researchers.
Their work suggests the health impact is stronger for women and that even "light" smokers face similar diseases to heavier smokers, including cancer.
The team tracked the health and death rates of almost 43,000 men and women from the mid 1970s up to 2002.
Their findings appear in the journal Tobacco Control, reports BBC.
According to Reuters, the researchers tracked the health and death records and smoking habits of the men and women, who had been screened for heart disease at the start of the study, from the 1970s to 2002.
They found very little difference in the risk of dying from cancer, apart from lung cancer. Men who were light smokers were about three times more likely to die of lung cancer than non-smokers.
In women the risk rose to five times higher.
The dangers of smoking are well documented. Previous research has shown that smokers die on average 10 years earlier than non-smokers but kicking the habit, even in middle age, can reduce the risk in half.
Smoking is also a risk factor for heart disease and stroke and raises the odds of developing age-related macular degeneration, which is the leading cause of blindness in the elderly.