Optimal Cardioprotective BMI for Adults with Type 2 Diabetes Could Vary by Age, New Study Suggests

Among adults with type 2 diabetes (T2D) older than age 65 years, a body mass index (BMI) in the “moderately overweight” range (26–28 kg/m²) may provide greater protection from cardiovascular disease (CVD)-related death than a BMI in the “normal” range. Middle-aged adults with T2D, however, are at the lowest risk of CVD mortality when their BMI is stable within the normal range of 23–25 kg/m².

The findings, from new research being presented at the 2024 European Congress on Obesity in Venice, Italy (May 12-15, 2024), are based on UK Biobank data from 22 874 participants with a diagnosis of T2D who were enrolled between 2006 and 2010. Given the known CV benefits for those with T2D of maintaining a healthy BMI, researchers, led by Shaoyong Xu, of Xiangyang Central Hospital, Affiliated Hospital of Hubei University of Arts and Science, China, were curious to understand whether optimal BMI in this population might vary by age.

Among the study cohort, the mean age was 59 years, and slightly more than half (59%) were women. Xu and colleagues used linked electronic health records to track CV health for a median of 12.5 years. There were 891 deaths related to CVD during that time.

Data were analyzed by age group—elderly (over age 65 years) and middle-age (age 65 years or younger). Researchers assessed the relationship between BMI, waist circumference, and waist-to-height ratio and the risk of CV death.

Hazard ratios were adjusted for traditional cardiometabolic risk factors and other factors associated with adverse CV outcomes including age, sex, smoking history, alcohol consumption, level of physical exercise, and history of CVD.

FINDINGS

In the group aged 65 years or younger, Xu et al found a BMI in the overweight range (25 kg/m² - 29.9 kg/m²) was associated with a 13% greater risk of death from CVD than among those with a BMI in the normal range (less than 25.0 kg/m²).

In contrast, among participants older than age 65 years the researchers reported that BMI in the overweight range was associated with an 18% lower risk of CVD-related mortality compared to having a BMI in the normal range.

Investigators described a U-shaped curve for the relationship between BMI and CV death that persisted after stratification by age, identifying different optimal BMI cutoffs for the 2 age groups: 24 kg/m² for those of middle-age and 27 kg/m² for the over 65 years group. The difference, authors said, suggests tailored approaches to care in the clinical setting.

On the other hand, researchers found a linear relationship between both waist circumference and waist-to-height ratio and the risk of CV death, a trend that also remained consistent by age group. However, no significant BMI cut-off point was identified.

“Importantly, we demonstrate that optimal BMI for people with type 2 diabetes varies by age, independent of traditional cardiometabolic risk factors,” Xu said in a press statement.

“Our findings suggest that for older individuals who are moderately overweight but not obese, maintaining rather than losing weight may be a more practical way of reducing their risk of dying from cardiovascular disease.”

He adds, “Our findings also indicate that adiposity may offer some protection against fatal diseases to some extent. The possible biological mechanisms that explain this ‘obesity survival paradox’ in elderly people may be associated with a lower rate of bone mass loss, which reduces the effects of fall and trauma episodes, and greater nutritional reserves to accommodate periods of acute stress.”

The authors say that in the future, measures of central obesity, such as waist circumference, could be used to further refine the risk.

XU et al point to the limitations inherent in an observational study and to several limitations of the findings. The number of CV deaths recorded was relatively small and no information was included regarding type of CVD or treatment. Also, the UK biobank cohort is majority White, limiting the applicability of findings to more diverse populations.

Also, classification errors may have been introduced by the nature of the cohort because anthropometric measurements were only assessed at the start of the study, and body weight may change during the follow-up period.

Source: UK Biobank study identifies ideal body weight for adults with type 2 diabetes to minimise risk of dying from cardiovascular disease. New release. European Association for the Study of Obesity. March 29, 2024. Accessed April 5, 2024. https://www.eurekalert.org/news-releases/1039372