Among current smokers, BMI is not consistently associated with increased stroke risk, and its impact is strongly modified by age, with findings suggesting that 'the potent vascular toxicity of smoking may overwhelm or alter typical weight-related risk pathways.'
Key Findings
Results
Stroke prevalence was highest among underweight smokers rather than obese smokers.
Stroke prevalence was 6.3% among underweight current smokers.
Data were drawn from 53,939 current adult smokers in the 2021 Behavioral Risk Factor Surveillance System (BRFSS).
This pattern contrasts with the general population expectation that higher BMI would be associated with higher stroke risk.
Survey-weighted logistic regression was used to estimate associations between BMI categories and self-reported stroke history.
Results
In adjusted models, the association between high BMI and stroke was attenuated or null among current smokers.
After adjustment for sociodemographic and health variables, higher BMI categories did not show a consistent positive association with stroke.
The study adjusted for potential confounders including sociodemographic and health variables.
Multicollinearity was assessed as part of the analytical approach.
The null or attenuated association suggests that smoking may overwhelm typical weight-related cardiovascular risk pathways.
Results
A significant interaction between BMI and age was identified, consistent with an 'obesity paradox' in older smokers.
Older obese smokers exhibited odds ratios near or below 1.0 for stroke.
Specifically, at ages 60-64, obese smokers had an OR of 0.70 (95% CI: 0.57-0.87) for stroke.
Interaction terms between BMI and age were formally tested to evaluate effect modification.
Results
Traditional cardiovascular risk factors did not mediate the BMI-stroke relationship in underweight or overweight smokers, with only partial mediation observed in obese smokers.
Exploratory decomposition analysis was used to assess mediation.
Hypertension and myocardial infarction showed only partial mediation of the BMI-stroke association in obese smokers.
No meaningful mediation by cardiovascular comorbidities such as hypertension and diabetes was found in underweight or overweight groups.
This finding suggests that standard cardiovascular intermediaries do not fully explain the BMI-stroke relationship among smokers.
Methods
The study utilized a large, nationally representative sample of current adult smokers from the 2021 BRFSS.
The analytic sample comprised 53,939 current adult smokers.
Data came from the 2021 Behavioral Risk Factor Surveillance System (BRFSS).
BMI was categorized as underweight, normal, overweight, and obese.
The outcome was self-reported stroke history.
Survey-weighted logistic regression was employed to account for the complex survey design.
Conclusions
The authors concluded that smoking cessation is reinforced as the primary preventive strategy given that smoking's vascular toxicity may overwhelm weight-related risk pathways.
The findings suggest that 'the potent vascular toxicity of smoking may overwhelm or alter typical weight-related risk pathways.'
BMI was not consistently associated with increased stroke risk among smokers.
The age-modified obesity paradox finding further complicates the role of BMI in stroke prevention among smokers.
Smoking cessation was identified as the primary preventive strategy rather than weight management alone.
What This Means
This research suggests that among people who currently smoke, being overweight or obese does not consistently increase the risk of stroke the way it does in the general population. Surprisingly, the highest stroke rates were found among underweight smokers (6.3%), and after accounting for other health and demographic factors, higher body weight was not clearly linked to greater stroke risk. The study analyzed data from nearly 54,000 current smokers across the United States using a large national health survey from 2021.
The study also found that age plays an important role in how body weight relates to stroke risk among smokers. In older smokers (for example, those aged 60-64), being obese was actually associated with lower stroke odds (OR 0.70), a phenomenon sometimes called the 'obesity paradox.' Additionally, common cardiovascular conditions like high blood pressure and heart attacks only partially explained the link between obesity and stroke in smokers, and did not explain it at all in underweight or overweight smokers.
This research suggests that smoking itself may be so damaging to blood vessels that it overrides the usual harmful effects of excess body weight on stroke risk. This means that for people who smoke, focusing solely on weight management may not be the most effective stroke prevention strategy. Instead, the findings reinforce that quitting smoking is the most important step smokers can take to reduce their stroke risk, regardless of their weight.
Alqahtani S, Aboonq M. (2026). Obesity's Role in Stroke Incidence Among Smokers: An Assessment of Confounding, Interaction, and Mediation Effects.. Saudi medical journal. https://doi.org/10.15537/1658-3175.8789