In the present large population-based cross-sectional study conducted in aged 60 years old population, BMI variability was associated with multimorbidity after adjusting for age, sex, race, education, sleep, smoking status, alcohol status, food security and physical activity. We also found that this relationship was significantly in higher BMI variability group.
Evidence for the adverse of both obesity and underweight on aging related chronic disease incidence was overwhelming and indisputable. Recently, several studies indicated that stable obesity across adulthood, weight gain from young to middle adulthood, and weight loss from middle to late adulthood were also associated with health problems. Lots of factors may cause weight changes, such as age, disease, or private habits. With aging, muscle loss can lead to sarcopenia or frailty, resulting in weight loss[10].Meanwhile, the incidence rate of aging related chronic diseases is significantly higher with aging, which may also lead to weight loss. In addition, fat mass can lead to weight gain, especially abdominal obesity. [11] Persons with a low level of education may have little awareness of healthy behaviors, or unable to manage their health. In this study we found that there were significant differences in age, education level, alcohol consumption and physical activity among different BMI variability groups. We also detected an interesting phenomenon that the group with small weight change has a higher BMI baseline level than the group with large weight change, and over time, the BMI level of the group with large weight change exceeds that of the group with small change. It is also speculated that the large change in body weight may be mainly due to the significant increase in body weight from middle age to older.
In addition to the obesity status at a single time point, more and more studies are now focusing on changes in body weight and health outcomes. A systematic review and meta-analysis of 26 cohort studies showed that both weight loss and weight gain from middle-aged to older adults were associated with increased risk of all cause and coronary vascular disease mortality.[12] In a meta-analysis, gain in BMI was positively associated with cancer risk [13] .Previous study also found that a high BMI is significantly related to asthma severity and prevalence, and that an increase in body silhouette between menarche and adulthood is related to the incidence of asthma later in life. [14,15] The mechanisms behind this association the decrease noted in the FEV /FVC ratio has potential relevance in the relationship between BMI and asthma. [16]Prescott E etal. [17] also revelled an important finding that a large proportion of subjects with COPD experiencing a weight loss and the increased mortality associated with this weight loss. The findings implied that maintaining normal weight across adulthood, especially preventing weight gain in early adulthood, important for preventing premature deaths in later life. [18]
Multimorbidity was defined by the presence of two or more chronic disease. Multimorbidity increased both with age and physical conditions, such as frailty, social deprivation, and obesity. [5,19,20]The prevalence of multimorbidity among the overweight or obese older population was from 36.61–44.64%[21]. Recently, several studies had shown increasing prevalence of overweight and obesity were related to increasing morbidity burden across different populations. A pooled analysis of 16 cohort studies from the USA and Europe found that compared with a healthy weight, the risk of developing cardiometabolic multimorbidity in overweight individuals was even more than ten times.[22] Helen P Booth et al. [23] reported that 32% of multimorbidity was attributable to overweight and obesity with a cross-sectional analysis. M. Jawed et al. [24] noted that adult populations with high obesity measures, including high BMI, body fat percentage (BF%) or visceral fat VF, carry a higher risk of multimorbidity, which increased substantially in the 60 to 69 years old group people.
In this study, we found that there was also a certain relationship between BMI variability and multimorbidity. The number of multimorbidity in high variation group was 1.35 times higher than that in low variation group. Stroke was the most common chronic disease that comorbidity with other chronic disease, followed by heart disease. Previous study showed that the excess risk of death due to adiposity increased with age, and the relative risk decreased with age because of dilution by the many other causes of death associated with increasing age. [25] Advanced age, female gender, negative life events, mental disorders, lower social economic status, lower education, tobacco, high risk waist hip ration, inactive physical actives, as well as overweight and obese were all risk factors associated with multimorbidity.[26,27] Chronic disease and smoking can themselves affect BMI, so in some prospective studies, smokers or participants who already have some chronic disease have been excluded. In our study, we did logistic analysis, after adjusting factors affecting comorbidity, such as age, sex, race, education, sleep, smoking status, alcohol status, food security and activity. We concluded that BMI variability was independently associated with incidence rate of multimorbidity, and it seems that higher weight variation showed a large response. But current study still did not fully understand how BMI variability was associated with the multimorbidity, so, more researches were needed.
There were still some limitations in our current study. First, our study was a cross-sectional study, which could not determine the cause and effect relationship between BMI variability and multimorbidity, and there is a need for prospective studies to provide more-definitive evidence. Second, there were some missing values of biochemical indexes such as low density lipoprotein, triglyceride, creatinine, and which could not be included in logistic analysis. Third, the onset time of each disease in this study was uncertain, and the specific time sequence of weight change and disease onset could not be determined. Finally, in this study, BMI information comes from patient- reported-outcome, which would led to information bias.
In conclusions, this study shows that there is a significant association between BMI variability and multimorbidity adjusting for other risk factors in elderly people. Maintaining normal BMI and avoiding significant changes in BMI is necessary for the elderly, or may reducing the incidence of comorbidity.