Sex-Related Differences in the Association Between Body Mass Index and Dementia Risk

The higher life expectancy of people in industrialized countries is accompanied by an increase in age-related diseases. This applies in particular to neurodegenerative diseases such as Alzheimer’s disease. As yet, there is no causal therapy for dementia; current therapy can only alleviate some symptoms in certain patients. In addition, the onset of dementia can be delayed by consistent treatment of the risk factors. This makes research into risk factors particularly important. One of these factors is obesity, which is known as a risk factor for numerous other diseases such as diabetes, cardiovascular diseases, and cancer. For example, previous studies have shown that obesity in midlife could increase dementia risk in later life. On the other hand, obesity in advanced age seems to be negatively associated with dementia [1]. However, little research has been done on sex-related differences in the association between body mass index (BMI) and dementia.

Zakharova and colleagues [2] analyzed sex-related differences in the association between BMI and dementia risk in 14,364 community-dwelling Japanese people aged between 40 and 74 years. This study found that underweight was strongly associated with a higher dementia risk (Hazard Ratio (HR): 2.26; 95% CI: 1.11–4.62) compared to overweight in men but not in women. In women, both BMI≤20.5 (underweight and low-normal) and BMI 25.0–29.9 (overweight) were associated with higher risk of dementia than in the reference group with BMI 22.8–24.9. However, the authors used different reference groups for women and men (overweight was the reference group in men, and high–normal BMI was the reference group in women) [2].

In the study conducted by Jacob et al. including 296,767 subjects followed in German general practices, authors also found sex-related differences in the association between BMI and the risk of dementia. In men, underweight was significantly associated with a higher risk of dementia as compared to normal weight. In women, overweight (versus normal weight) was significantly associated with a lower dementia risk (HR = 0.93, 95% CI = 0.88–0.97) [3].

Both studies clearly suggest that BMI, especially underweight, may be associated with increased dementia risk but that this association differs in women and men. While Zakharova et al. [2] emphasized the term risk in their work and concluded that sex-related differences in adiposity might be involved in the development of dementia, Jacobs et al. [3] wrote more cautiously about associations. These associations can be caused by other factors and BMI may not be directly involved in the development of dementia. Nevertheless, both studies are important for the discovery of sex-related associations between weight and dementia, and they form the basis for further research in this area.