Abstract
OBJECTIVE To evaluate the combined associations of diet, physical activity, moderate alcohol consumption, and smoking with body weight on risk of all cause and cause specific mortality. DESIGN Longitudinal study with up to 32 years of follow-up. SETTING Nurses’ Health Study (1980-2012) and Health Professionals Follow-up Study (1986-2012). PARTICIPANTS 74582 women from the Nurses’ Health Study and 39 284 men from the Health Professionals Follow-up Study who were free from cardiovascular disease and cancer at baseline. MAIN OUTCOME MEASURES Exposures included body mass index (BMI), score on the alternate healthy eating index, level of physical activity, smoking habits, and alcohol drinking while outcome was mortality (all cause, cardiovascular, cancer). Cox proportional hazard models were used to calculate the adjusted hazard ratios of all cause, cancer, and cardiovascular mortality with their 95% confidence intervals across categories of BMI, with 22.5-24.9 as the reference. RESULTS During up to 32 years of follow-up, there were 30 013 deaths (including 10 808 from cancer and 7189 from cardiovascular disease). In each of the four categories of BMI studied (18.5-22.4, 22.5-24.9, 25-29.9, ≥30), people with one or more healthy lifestyle factors had a significantly lower risk of total, cardiovascular, and cancer mortality than individuals with no low risk lifestyle factors. A combination of at least three low risk lifestyle factors and BMI between 18.5-22.4 was associated with the lowest risk of all cause (hazard ratio 0.39, 95% confidence interval 0.35 to 0.43), cancer (0.40, 0.34 to 0.47), and cardiovascular (0.37, 0.29 to 0.46) mortality, compared with those with BMI between 22.5-24.9 and none of the four low risk lifestyle factors. CONCLUSION Although people with a higher BMI can have lower risk of premature mortality if they also have at least one low risk lifestyle factor, the lowest risk of premature mortality is in people in the 18.5-22.4 BMI range with high score on the alternate healthy eating index, high level of physical activity, moderate alcohol drinking, and who do not smoke. It is important to consider diet and lifestyle factors in the evaluation of the association between BMI and mortality.
Generated Summary
This prospective cohort study investigated the combined associations of diet, physical activity, moderate alcohol consumption, and smoking with body weight on the risk of all-cause and cause-specific mortality. The study utilized data from the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS). Participants included 74,582 women from the NHS and 39,284 men from the HPFS who were free from cardiovascular disease and cancer at baseline. The study assessed body mass index (BMI), adherence to the alternate healthy eating index, physical activity levels, smoking habits, and alcohol consumption. The primary outcomes were all-cause mortality, cardiovascular mortality, and cancer mortality. Cox proportional hazard models were used to calculate the adjusted hazard ratios across different BMI categories, with a reference group of 22.5-24.9 BMI. The study’s duration was up to 32 years of follow-up, offering a comprehensive view of the long-term associations between lifestyle factors, BMI, and mortality. The research aimed to evaluate how combinations of lifestyle factors and body weight influence mortality risk, going beyond the conventional focus on BMI as an isolated factor. The research recognizes the U-shaped relationship between BMI and mortality observed in many epidemiological studies. The data from this research also suggests that being overweight and obese individuals can benefit from adopting low-risk lifestyle behaviors to significantly reduce the risk of premature mortality.
Key Findings & Statistics
- During the follow-up period (up to 32 years), there were 30,013 deaths, including 10,808 from cancer and 7,189 from cardiovascular disease.
- The study found a U-shaped relationship between BMI and mortality in the overall population.
- In the different BMI categories (18.5-22.4, 22.5-24.9, 25-29.9, and ≥30), individuals with one or more healthy lifestyle factors had a significantly lower risk of total, cardiovascular, and cancer mortality compared to those with no low-risk lifestyle factors.
- A combination of at least three low-risk lifestyle factors and a BMI between 18.5-22.4 was associated with the lowest risk of all-cause mortality (hazard ratio 0.39, 95% CI 0.35 to 0.43), cancer mortality (hazard ratio 0.40, 95% CI 0.34 to 0.47), and cardiovascular mortality (hazard ratio 0.37, 95% CI 0.29 to 0.46).
- In the Nurses’ Health Study (NHS, 1980-2012) and Health Professionals’ Follow-up Study (HPFS, 1986-2012):
- Age-adjusted HR (95% CI) for all-cause mortality was 2.22 (2.03 to 2.43) for BMI <18.5 in NHS and 1.69 (1.36 to 2.09) in HPFS, 1.13 (1.08 to 1.17) and 1.07 (1.01 to 1.13) for BMI 18.5-22.4, 1.0 in both cohorts for BMI 22.5-24.9, 1.06 (1.02 to 1.11) and 1.06 (1.01 to 1.11) for BMI 25.0-27.4, 1.14 (1.08 to 1.21) and 1.26 (1.18 to 1.33) for BMI 27.5-29.9, 1.32 (1.25 to 1.39) and 1.52 (1.42 to 1.63) for BMI 30.0-34.9, 1.86 (1.73 to 2.01) and 2.12 (1.82 to 2.47) for BMI 35.0-39.9, and 2.52 (2.27 to 2.79) and 2.77 (2.17 to 3.54) for BMI ≥40.
- The hazard ratios for all-cause mortality, stratified by the number of low-risk lifestyle factors, showed that with no low-risk factors: the hazard ratio was 2.37 (2.08 to 2.69) for BMI <18.5, 1.24 (1.17 to 1.32) for BMI 18.5-22.4, 1.0 for BMI 22.5-24.9, 1.03 (0.96 to 1.10) for BMI 25.0-27.4, 1.03 (0.96 to 1.10) for BMI 27.5-29.9, 1.11 (1.03 to 1.19) for BMI 30.0-34.9, 1.50 (1.34 to 1.68) for BMI 35.0-39.9, and 1.80 (1.53 to 2.11) for BMI ≥40.
- With one low-risk factor: the hazard ratio was 1.89 (1.65 to 2.16) for BMI <18.5, 1.11 (1.06 to 1.17) for BMI 18.5-22.4, 1.0 for BMI 22.5-24.9, 0.98 (0.94 to 1.06) for BMI 25.0-27.4, 1.11 (1.05 to 1.18) for BMI 27.5-29.9, 1.22 (1.15 to 1.30) for BMI 30.0-34.9, 1.59 (1.44 to 1.75) for BMI 35.0-39.9, and 2.13 (1.84 to 2.45) for BMI ≥40.
- With two low-risk factors: the hazard ratio was 1.57 (1.27 to 1.94) for BMI <18.5, 1.05 (0.97 to 1.13) for BMI 18.5-22.4, 1.0 for BMI 22.5-24.9, 1.00 (0.95 to 1.05) for BMI 25.0-27.4, 1.03 (0.96 to 1.10) for BMI 27.5-29.9, 1.22 (1.15 to 1.30) for BMI 30.0-34.9, 1.64 (1.41 to 1.91) for BMI 35.0-39.9, and 2.40 (1.89 to 3.05) for BMI ≥40.
- With three or four low-risk factors: the hazard ratio was 0.92 (0.77 to 1.91) for BMI <18.5, 1.00 (0.94 to 1.06) for BMI 18.5-22.4, 1.0 for BMI 22.5-24.9, 0.96 (0.84 to 1.09) for BMI 25.0-27.4, 1.13 (1.03 to 1.23) for BMI 27.5-29.9, 1.35 (1.22 to 1.48) for BMI 30.0-34.9, 1.00 (0.78 to 1.29) for BMI 35.0-39.9, and 3.50 (2.00 to 6.13) for BMI ≥40.
Other Important Findings
- The lowest risk of premature mortality was observed in individuals with a BMI between 18.5 and 22.4, especially when combined with a high score on the alternate healthy eating index, high levels of physical activity, moderate alcohol consumption, and non-smoking.
- Among overweight and obese individuals, those who adopted one or more low-risk lifestyle behaviors had a significantly reduced risk of premature mortality.
- The study highlights that the U-shaped relationship between BMI and mortality may be driven by the over-representation of individuals who are lean due to chronic metabolic and pathological conditions, smoking, sedentary lifestyles, and unhealthy diets.
Limitations Noted in the Document
- The study population consisted primarily of health professionals, mainly white men and women, which may limit the generalizability of the findings.
- Measurement errors in self-reported lifestyle factors are inevitable in prospective studies; however, these are typically unrelated to the outcomes and are likely to have attenuated the observed associations.
Conclusion
The study’s findings emphasize the importance of considering lifestyle factors when evaluating the relationship between BMI and mortality. The lowest risk of premature mortality was observed in individuals with a BMI between 18.5 and 22.4, particularly when combined with a healthy lifestyle. The study suggests that interventions promoting a healthy lifestyle, including physical activity, a balanced diet, moderate alcohol consumption, and smoking cessation, are crucial for reducing mortality risk. The research underscores that the U-shaped relationship between BMI and mortality may be influenced by factors such as chronic diseases, smoking, and unhealthy dietary patterns. The study highlights the significant benefits of healthy lifestyles, even for individuals who are overweight or obese, indicating that the adoption of low-risk lifestyle behaviors can substantially reduce their risk of premature mortality. The study’s conclusion supports that leanness induced by healthy lifestyles is the optimal way to promote healthy longevity and to reduce the risk of premature death.