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The prevalence of diabetes, heart disease, and stroke multimorbidity (co-occurrence of two or three of these conditions) has increased rapidly. Little is known about how the three conditions progress from one to another sequentially through the life course. We aimed to delineate this progression in middle-aged women and to determine the roles of common risk factors in the accumulation of diabetes, heart disease, and stroke multimorbidity.

Methods and findings

We used data from 13,714 women aged 45–50 years without a history of any of the three conditions. They were participants in the Australian Longitudinal Study on Women's Health (ALSWH), enrolled in 1996, and surveyed approximately every 3 years to 2016. We characterized the longitudinal progression of the three conditions and multimorbidity. We estimated the accumulation of multimorbidity over 20 years of follow-up and investigated their association with both baseline and time-varying predictors (sociodemographic factors, lifestyle factors, and other chronic conditions).
Over 20 years, 2,511 (18.3%) of the women progressed to at least one condition, of whom 1,420 (56.6%) had diabetes, 1,277 (50.9%) had heart disease, and 308 (12.3%) had stroke; 423 (16.8%) had two or three of these conditions. Over a 3-year period, the age-adjusted odds of two or more conditions was approximately twice that of developing one new condition compared to women who did not develop any new conditions. For example, the odds for developing one new condition between Surveys 7 and 8 were 2.29 (95% confidence interval [CI], 1.93–2.72), whereas the odds for developing two or more conditions was 6.51 (95% CI, 3.95–10.75). The onset of stroke was more strongly associated with the progression to the other conditions (i.e., 23.4% [95% CI, 16.3%–32.2%] of women after first onset of stroke progressed to other conditions, whereas the percentages for diabetes and heart disease were 9.9% [95% CI, 7.9%–12.4%] and 11.4% [95% CI, 9.1%–14.4%], respectively). Being separated, divorced, or widowed; being born outside Australia; having difficulty managing on their available income; being overweight or obese; having hypertension; being physically inactive; being a current smoker; and having prior chronic conditions (i.e., mental disorders, asthma, cancer, osteoporosis, and arthritis) were significantly associated with increased odds of accumulation of diabetes, heart disease, and stroke multimorbidity. The main limitations of this study were the use of self-reported data and the low number of events.

Conclusions
Stroke was associated with increased risk of progression to diabetes or heart disease. Social inequality, obesity, hypertension, physical inactivity, smoking, or having other chronic conditions were also significantly associated with increased odds of accumulating multimorbidity. Our findings highlight the importance of awareness of the role of diabetes, heart disease, and stroke multimorbidity among middle-aged women for clinicians and health-promotion agencies.

Author summary

Why was this study done?

• In an aging population, it is common for women to experience two or more of diabetes, heart disease, and stroke.
• Few published studies have investigated how women progress from a “healthy” state to having one of diabetes, heart disease, and stroke and then to multimorbidity.
• No prospective evidence is available on the roles of time-varying common risk factors (i.e., high blood pressure or obesity) in the accumulation of multimorbidity from diabetes, heart disease, and stroke—information that may be important for health promotion and risk modification.

What did the researchers do and find?

• In this national prospective cohort study, 13,714 middle-aged Australian women (45–50 years old) were recruited in 1996 and have been followed for 2 decades. We collected data on their health conditions, including diabetes, heart disease, and stroke, as well as potential risk factors every 3 years until 2016.
• From early to late middle age, many more women developed a single condition than multimorbidity. However, the odds ratio for accumulation of multimorbidity (i.e., from none or one to two or three, or from two to three of diabetes, heart disease, or stroke) was much higher than the odds of developing only one new condition, compared to women who did not develop any new condition over 3 years.
• Nearly one-quarter of women who were initially diagnosed with stroke subsequently progressed to other conditions, a much higher percentage than those who were initially diagnosed with diabetes (9.9%) or heart disease (11.4%).
• Women who were obese, had hypertension, were physically inactive, were smokers, or had other chronic conditions had higher odds of accumulating diabetes, heart disease, and stroke multimorbidity over the following 3-year period than women without these characteristics.

What do these findings mean?

• To our knowledge, this is the first study to delineate the accumulation of diabetes, heart disease, and stroke multimorbidity and investigate its association with both baseline and time-varying predictors in a prospective cohort study.
• These findings suggest that health promotion, interventions for modifying lifestyle factors (obesity, high blood pressure, physical inactivity, and smoking), and treatment of other chronic conditions would be potentially beneficial for preventing the accumulation of diabetes, heart disease, and stroke multimorbidity.
• For women who have had a stroke, health promotion, intervention, and treatment would be particularly important, as they appear most likely to progress to other conditions