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. 2022 Apr;53(4):1301-1309.
doi: 10.1161/STROKEAHA.121.034782. Epub 2021 Nov 10.

Obesity Does Not Protect From Subarachnoid Hemorrhage: Pooled Analyses of 3 Large Prospective Nordic Cohorts

Ilari Rautalin  1   2 , Jaakko Kaprio  2   3 , Tor Ingebrigtsen  4   5 , Pekka Jousilahti  6 , Maja-Lisa Løchen  7 , Pål Richard Romundstad  8 , Veikko Salomaa  6 , Anne Vik  9   10 , Tom Wilsgaard  7 , Ellisiv B Mathiesen  11   12 , Marie Sandvei  8   13 , Miikka Korja  1
Affiliations

Obesity Does Not Protect From Subarachnoid Hemorrhage: Pooled Analyses of 3 Large Prospective Nordic Cohorts

Ilari Rautalin et al. Stroke. 2022 Apr.

Abstract

Background: Several population-based cohort studies have related higher body mass index (BMI) to a decreased risk of subarachnoid hemorrhage (SAH). The main objective of our study was to investigate whether the previously reported inverse association can be explained by modifying effects of the most important risk factors of SAH-smoking and hypertension.

Methods: We conducted a collaborative study of three prospective population-based Nordic cohorts by combining comprehensive baseline data from 211 972 adult participants collected between 1972 and 2012, with follow-up until the end of 2018. Primarily, we compared the risk of SAH between three BMI categories: (1) low (BMI<22.5), (2) moderate (BMI: 22.5-29.9), and (3) high (BMI≥30) BMI and evaluated the modifying effects of smoking and hypertension on the associations.

Results: We identified 831 SAH events (mean age 62 years, 55% women) during the total follow-up of 4.7 million person-years. Compared with the moderate BMI category, persons with low BMI had an elevated risk for SAH (adjusted hazard ratio [HR], 1.30 [1.09-1.55]), whereas no significant risk difference was found in high BMI category (HR, 0.91 [0.73-1.13]). However, we only found the increased risk of low BMI in smokers (HR, 1.49 [1.19-1.88]) and in hypertensive men (HR, 1.72 [1.18-2.50]), but not in nonsmokers (HR, 1.02 [0.76-1.37]) or in men with normal blood pressure values (HR, 0.98 [0.63-1.54]; interaction HRs, 1.68 [1.18-2.41], P=0.004 between low BMI and smoking and 1.76 [0.98-3.13], P=0.06 between low BMI and hypertension in men).

Conclusions: Smoking and hypertension appear to explain, at least partly, the previously reported inverse association between BMI and the risk of SAH. Therefore, the independent role of BMI in the risk of SAH is likely modest.

Keywords: blood pressure; body mass index; hypertension; smoking; subarachnoid hemorrhage.

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Conflict of interest statement

Dr Salomaa has received honoraria from Novo Nordisk and Sanofi for consulting and also has an ongoing research collaboration with Bayer Ltd (all unrelated to the present study). The other authors report no conflicts.

Figures

Figures 1.
Figures 1.
Body mass index (BMI) and the risk of subarachnoid hemorrhage (SAH). All models were adjusted for age, sex, smoking, systolic blood pressure, study cohort, and study year. A, Adjusted hazard ratios (HRs; dots) and 95% CIs (whiskers) for SAH by BMI units. The BMI range 18–21 was used as a reference group. B, Adjusted HRs (dots) and 95% CIs (whiskers) for SAH by the low and high BMI categories. The moderate category was used as the reference group. C, The cumulative incidence of SAH by the BMI categories in the presence of competing risk by other causes of death.
Figure 2.
Figure 2.
Body mass index (BMI) and the risk of subarachnoid hemorrhage (SAH) by hypertension subgroups. A, Hypertension rates by BMI in the entire cohort (black connected line) and in the SAH cases (gray connected line). These relationships were similar in all 3 study cohorts, in both men and women, and were not dependent on age. B, Adjusted hazard ratios (HRs; dots) and 95% CIs (whiskers) for SAH in men and women with low BMI. Moderate BMI category serves as a reference group. The estimates are presented by sex and hypertension status at baseline. Models are adjusted for age, sex, smoking, study cohort, and study year. C, Adjusted HRs (dots) and 95% CIs (whiskers) for SAH in hypertensive participants by BMI categories. Normotensive participants represent the reference category. Adjusted models included variables of age, sex, smoking, study cohort, and study year.
Figure 3.
Figure 3.
Body mass index (BMI) and the risk of subarachnoid hemorrhage (SAH) by smoking subgroups. A, Smoking rates by BMI in the entire cohort (black connected line) and in the SAH cases (gray connected line). These relationships were seen in all three study cohorts, in both men and women, and were not dependent on age. B, Adjusted hazard ratios (HRs; dots) and 95% CIs (whiskers) for SAH in men and women with low and high BMI. The moderate BMI category was used as a reference group. The estimates are presented by sex and by smoking status at baseline. The models were adjusted for age, sex, systolic blood pressure, study cohort, and study year. C, Adjusted HRs (dots) and 95% CIs (whiskers) for SAH in current smokers by BMI categories in men and women. Never/former smokers represent the reference category. The models were adjusted for age, sex, systolic blood pressure, study cohort, and study year.
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