The use of smokeless tobacco products was associated with an increased risk for fatal myocardial infarction (MI) and stroke, a meta-analysis found.
For fatal MI, the relative risk associated with ever having used these products was 1.13 (95% CI 1.06 to 1.21), according to Paolo Boffetta, MD, and Kurt Straif, MD, PhD, of the International Agency for Research on Cancer in Lyon, France.
And the overall relative risk for fatal stroke was 1.40 (95% CI 1.28 to 1.54), the researchers reported online in the BMJ.
The use of oral and nasal smokeless tobacco products such as snuff and chewing tobacco has increased in recent decades, particularly among people younger than 40, based on claims of less health risk than smoking.
Recently, North American and Scandinavian researchers found an increased risk of oropharyngeal and prostate cancers.
But smokeless tobacco does pose potential health risks related to MI and stroke, possibly because of increases in blood pressure and heart rate, as well as associations with diabetes, metabolic syndrome, and obesity, according to the investigators.
"Determining the role of smokeless tobacco in cardiovascular diseases is important," they wrote, "given the high incidence and mortality from these diseases."
They therefore undertook a systematic review that included 11 studies, eight from Sweden and three from the U.S.
Eight were prospective cohort studies, three were population-based case-control studies, and nine included only subjects who had never smoked tobacco. Most included only men.
Among the nine studies that estimated risk for any MI, the risk associated with ever having used smokeless tobacco was 0.99 (95% CI 0.89 to 1.10).
The lack of association with any MI included both current and former users, and when the analysis was restricted to cohort studies the relative risk for any MI was 1.04 (95% CI 0.95 to 1.14).
Among the eight studies estimating risk for fatal MI, the excess risk was present only for current, not former, smokeless tobaccouse.
Based on six risk estimates, the overall risk of any stroke was 1.19 (95% CI 0.97 to 1.47), with increased risk being seen only for current use.
In the sole study that investigated risk according to duration or frequency of use, no significant trend was seen for fatal stroke, but the relative risk was higher among those with a long history of use.
And in the single study that reported stroke risk by type of event, the relative risk was higher for fatal ischemic stroke (RR 1.63, 95% CI 1.02 to 2.62) than for fatal hemorrhagic stroke (RR 1.05, 95% CI 0.61 to 1.80).
The risks for fatal MI and stroke were seen in studies both from the U.S. and Sweden.
The proportion of deaths from MI that was attributable to smokeless tobacco products was 0.5% in the U.S. and 5.6% in Sweden, while the corresponding numbers for stroke were 1.7% and 5.4%.
The researchers noted potential sources of bias such as the inclusion of case-control studies, confounding by active smoking, and misclassification of users, but they found no strong evidence for effects of bias.
"If the association is real, its public health and clinical implications might be substantial, despite the fact that the magnitude of the excess risk is small," they wrote.
Further research should attempt to determine how smokeless tobacco products affect the cardiovascular system and to investigate further if risk is also elevated for nonfatal events.
The study received no funding and the investigators declared no competing interests.
