Background:
Prior work has shown that fibrinogen, a well-known inflammatory marker, is associated with cardiovascular (CV) events. While it is known that physical activity (PA) imparts CV health benefits, there remains a knowledge gap on the interactions of PA with systemic inflammation on risk of CV death among American Indians.
Hypothesis:
To investigate the relationship between PA, inflammation, and CV death, we tested the hypotheses that: (i) PA is associated with lower risk of CV death, and (ii) the CV benefit of PA is mediated via an inflammatory pathway.
Methods:
We examined the association between PA (leisure-time plus occupational as METs[Metabolic Equivalent of Task]-hours per week via a validated questionnaire) and CV death among 3,135 adults (mean age 56 ± 8) without baseline CV disease in Strong Heart Study (1989-1991), a longitudinal study among American Indians. Preacher and Hayes bootstrap method was used for the model assessing mediation by fibrinogen.
Results:
During 26 years (mean 17.3 ± 8 years) of follow-up, there were 378 CV deaths. Compared to participants with minimal activity, subjects with higher levels of PA had a lower risk of CV death. Odds ratios were 0.91 (95% confidence interval [CI]: 0.65-1.21), 0.69 (95% CI: 0.51-0.92), and 0.56 (95% CI: 0.39-0.71) (p-trend=0.003), for increasing quartile of activity compared to the lowest, after adjustment for age, sex, study site, education, smoking, diabetes, hypertension, BMI, LDL cholesterol, and urine albumin-creatinine ratio. Mediation analysis showed the effect of PA on CV death was fully mediated via fibrinogen level (correlation coefficient: 0.998, 95% CI 0.995-0.999; Sobel test z= -3.11, p=0.03) (Figure).
Conclusion:
In a population-based study of American Indians, PA compared to inactivity, was associated with lower risk of CV death. This study highlights that PA is associated with improved CV outcomes and this effect is largely driven by inflammation.
Cancer mortality in a population-based cohort of American Indians – The strong heart study
