HEALTHY LIFESTYLE AND RISK OF MULTIMORBIDITY

Background Life expectancy has increased worldwide going from 45.7 years in 1950 to 72.6 years in 2019. A subgroup of these, chronic diseases (i.e., health problems requiring ongoing management over a period of years or decades), may lead to challenges in patient care when they present concomitantly (i.e., as multimorbidity). Because clinical trials often exclude patients with multimorbidity and most guidelines do not provide recommendations for multimorbid patients, these challenges persist. Moreover, multimorbidity negatively affects quality of life and functional ability and accelerates mortality. Many studies have been published on the role of modifiable lifestyle factors on multimorbidity, i.e., of tobacco and alcohol consumption, being overweight or obese, having a poor diet, and a low physical activity level. To our knowledge, only one study combined them in a comprehensive total lifestyle score. Therefore, a gap remains regarding the role of multiple lifestyle habits combined on multimorbidity. Aim Our aim was: i) to determine the patterns of multimorbidity of selected groups of diseases or conditions, chosen among the major causes of death. and ii) to estimate the effect of five important modifiable lifestyle behaviors on the morbidity and multimorbidity of the selected diseases or conditions. Methods To define multimorbidity we considered all chronic causes of death among the 369 diseases, injuries, and impairments recorded in the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) publicly available databases. We ranked the causes of death by decreasing yearly rates and grouped them as follows: 1) Cardiovascular diseases, i.e., ischemic heart disease, stroke, and hypertensive heart disease; 2) Gastrointestinal tract (GIT) cancers (i.e., colorectal, gastric, liver, pancreatic, and esophageal cancers) and respiratory tract (RT) cancers (i.e., trachea, bronchus, and lung cancers); 3) Alzheimer disease and other dementias; 4) Chronic obstructive pulmonary disease. These four macro-groups of chronic diseases are together responsible for an average cause-specific crude mortality rate of 827 deaths per thousand inhabitants. Multimorbidity was defined as the occurrence of diseases from two different groups. We used data from the Swedish National March Cohort (SNMC) to study the association of five lifestyle factors with multimorbidity. We developed a partial healthy lifestyle index (HLI) score for each of the lifestyle exposures and a total HLI score ranging from 0 (worst habits) to 20 (best habits). Four states (i.e., baseline, morbidity, multimorbidity, and death) were used to define a multi-state framework, and each transition was modelled individually with a parametric multi-state model. We estimated transition probability between states and hazard ratios (HRs) and 95% confidence intervals (CIs) for the exposures of interest. Results During an average follow-up time of 18.2 years we observed 6,458 morbidity cases, 946 transitions to multimorbidity, and 4,441 deaths. For values of the five partial HLI scores corresponding to healthier lifestyles we observed a reduction in the risk of morbidity, multimorbidity, and mortality, and we found that, e.g., over 15 years of follow-up, a man aged 65 years at baseline with an excellent lifestyle (all partial scores 4) would have a 33% reduction in the cumulative probability of morbidity, multimorbidity, and death combined compared to another man with same characteristics but a poor lifestyle (all partial scores 0-1). In case of women, the cumulative probability would be reduced by 29%. One unit increase in the total HLI score corresponded to 4% reduction in the risk of morbidity (HR [95% CI]: 0.96 [0.95-0.97]) and 6% in the risk of multimorbidity (0.94 [0.92-0.96]), similarly for both males and females. Having an HLI score of 16-20 halved the risk of morbidity compared to an HLI of 0-4 (HR [95% CI]: 0.47 [0.36-0.61] in men, and 0.46 [0.33-0.64] in women) with a stronger effect for women (p-value for heterogeneity 0.01), and reduced the risk of multimorbidity by two thirds (0.35 [0.20-0.63] in men and 0.30 [0.16-0.56] in women; p-value for heterogeneity <0.01). Conclusions We found that healthy lifestyle habits, summarized by the HLI score, were inversely associated with morbidity and multimorbidity of selected cardiovascular diseases, gastrointestinal and respiratory cancers, dementia, and COPD. We determined that being a never smoker or quitting smoking, having a low alcohol consumption, high physical activity levels, and a low BMI, and following the Mediterranean Diet recommendations can lower the probability of morbidity, multimorbidity and death. This effect is particularly evident when all the healthy lifestyles are combined.