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Stroke, CHD risk persist with minimal cigarette consumption
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Smoking just one to five cigarettes per day carries a larger risk for CHD and stroke than previously expected, according to data published in BMJ.
“Some experts were already aware of the higher-than-expected risk for heart disease for light smoking, which has come from individual studies. Many smokers cut down instead of quitting, and surveys show that a proportion of people believe that light smoking carries little or no harm,” Allan Hackshaw, MSc, from the Cancer Research UK & UCL Cancer Trials Centre at the University College London, told Cardiology Today. “We therefore felt it was important to obtain a reliable evidence base on this by combining all the studies together. Also, we wanted to look at whether the same finding applies to stroke — not often examined before.”
To quantify the risk for CHD and stroke for light smoking using the relationship between cigarette consumption and CVD, the researchers conducted a systematic literature review of articles published between 1946 and May 2015 consisting of 141 cohort studies from 55 publications.
For each study, regression modeling between risk and cigarette consumption was used to estimate the RR for smoking one, five or 20 cigarettes daily.
Analyses were adjusted for age and often additional confounders.
The primary measure of the study was the excess RR for smoking one cigarette per day expressed as a proportion of that for smoking 20 cigarettes per day, expected to be about 5% assuming a linear relation between risk and consumption, as has been seen with lung cancer.
In a random-effects meta-analysis, the researchers pooled RRs for people smoking one, five and 20 cigarettes per day compared with those who never smoked. Hackshaw and colleagues conducted separate analyses for each combination of sex and disorder.
CHD risk
The pooled RR for CHD among men was 1.48 (95% CI, 1.3-1.69) for smoking one cigarette per day and 2.04 (95% CI, 1.86-2.24) for 20 cigarettes per day, using all studies, but 1.74 (95% CI, 1.5-2.03) for one cigarette per day and 2.27 (95% CI, 1.9-2.72) among studies in which the RR had been adjusted for multiple confounders.
Among women, the pooled RRs for CHD were 1.57 (95% CI, 1.29-1.91) and 2.84 (95% CI, 2.21-3.64) for one and 20 cigarettes per day, respectively, and 2.19 (95% CI, 1.84-2.61) for one cigarette per day and 3.95 (95% CI, 3.34-4.67) for 20 cigarettes per day using RRs adjusted for multiple factors.
According to the researchers, men who smoked one cigarette per day had 46% of the excess RR for smoking 20 cigarettes per day (53% using RRs adjusted for multiple factors), and women had 31% of the excess risk (38% using RRs adjusted for multiple factors).
Stroke risk
The pooled RRs for stroke in men was 1.25 (95% CI, 1.13-1.38) for smoking one cigarette per day and 1.64 (95% CI, 1.48-1.82) for smoking 20 cigarettes per day. After adjustment for multiple factors, the RRs were 1.3 for one cigarette per day (95% CI, 1.11-1.53) and 1.56 for 20 cigarettes per day (95% CI, 1.31-1.86), according to the researchers.
For women, the pooled RRs for stroke were 1.31 (95% CI, 1.13-1.52) for one cigarette per day and 2.16 (95% CI, 1.69-2.75) for 20 cigarettes per day. After adjustment, the pooled RRs were 1.46 (95% CI, 1.2-1.78) for one cigarette per day and 2.42 (95% CI, 1.67-3.52) for 20 cigarettes per day.
The excess risk for stroke linked to one cigarette per day, relative to 20 cigarettes per day, was 41% for men and 34% for women, rising to 64% for men and 36% for women using RRs adjusted for multiple factors, the researchers wrote.
They noted that RRs were generally higher among women than men.
“Cutting down is certainly better than not doing so, and should be encouraged by health professionals, because this greatly reduces the risk for cancer and other disorders. Although the risk of cardiovascular disease also reduces, it is nowhere near as much as many intuitively expect,” Hackshaw said in an interview. “So, if smokers wish to avoid most of the excess risk of cardiovascular disease (due to smoking), they should go further and stop completely. And they could use whatever effective cessation aid that suits them, including e-cigarettes — considered by many to be much safer than cigarettes — and long-term studies are in progress on this.”
According to Hackshaw, cardiologists should continue to try to encourage smokers to quit, and they could clarify their information by referring to the significant harms still linked to light smoking.
“The next steps are probably around still finding helpful ways of getting people to quit,” he said. “This includes more evidence on the harms of e-cigarettes, and if there are any, they would need to be balanced against those for continued smoking, including light smoking.”– by Dave Quaile
Disclosures: The authors report no relevant financial disclosures.
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