A new study published in The Lancet explores shifting mortality rates and mortality associations with body mass index (BMI) in England between 2004 and 2019.
Study: Trends in all-cause and cause-specific mortality by BMI levels in England, 2004–2019: a population-based primary care records study. Image Credit: Ljupco Smokovski / Shutterstock.com
Introduction
The prevalence of obesity tripled to 13% from 1975 to 2016. In 2019, obesity caused approximately five million deaths, most of which were due to non-communicable diseases (NCDs), including cardiometabolic disorders and cancer.
Between 2007 and 2017, all-cause and NCD mortality rates were reduced by 14% and 7%, respectively, primarily because of declining cardiovascular disease (CVD) mortality. However, the 40% reduction in CVD deaths in the 2000s was followed by a sharp decline, resulting in annual reductions of less than 2%.
The current study examines the role of obesity in these fluctuating mortality rates based on primary care records obtained between 2004 and 2019 from the Clinical Practice Research Datalink. Data from 880,683 individuals with one or more BMI measurements between 1999 and 2014 and subsequent follow-up visits were included in the analysis.
Shifts in all-cause mortality
Over 25% of normal-weight and overweight individuals, as well as 20% of obese individuals, were from the highest socioeconomic quintile. Smokers and ex-smokers were over-represented in the normal weight and other two categories, respectively.
Obese individuals had higher all-cause mortality as compared to those who were overweight or normal weight. However, mortality rates declined more rapidly among obese individuals over time, which resulted in a lower rate of all-cause mortality.
The average annual reduction in all-cause mortality rates among obese males was about 3% every year, with a shift from 23 to 15 deaths for every 1,000 person-years (PY) from 2004 to 2019, respectively.
Among normal-weight and overweight individuals, average annual all-cause mortality rates declined by 2% each year. For obese females, this mortality rate was reduced by 2% each year from 13 to nine for every 1,000 PY. CVD deaths declined more sharply than all-cause mortality rates across all BMI categories.
NCD mortality
Males
In obese males, CVD deaths were reduced by 7% each year, from 12 to four deaths for every 1,000 PY as compared 5% reductions each year for normal weight and overweight males.
Non-CVD, non-cancer NCD death rates increased by 2% every year among overweight males. Liver- and endocrine-related deaths decreased by 90% and 12% each year, respectively, for normal-weight males.
Neurological mortality increased irrespective of sex and BMI. Nevertheless, obese males experienced a 300% increase in neurological mortality from less than 0.0001 to 0.87 for every 1,000 PY as compared to 7% and 9% of overweight and normal-weight males, respectively.
Females
Among obese and overweight females, CVD mortality declined by 4% each year from six to three for every 1,000 PY, respectively, as compared to 2% among normal-weight females. No changes in cancer mortality rates were observed.
NCD mortality increased by 4% and 6% for normal-weight and overweight women, respectively, without any change observed for obese women.
Neurological deaths increased for normal weight and overweight women at 17% and 15% each year, respectively. Liver-related mortality increased among obese females by nearly 1,000% every year from less than 0.0001 to 0.042 for every 1,000 PY. Endocrine-related deaths declined by 11% each year.
Causes of death in males
By 2019, cancers were the leading cause of death in all males and overweight females. CVD deaths accounted for 45-54% of deaths in 2004 and declined to 25-30% in 2019.
Cancer was responsible for 30% and 27% of deaths among normal-weight people in 2004 and 2019, respectively. For obese and overweight individuals, cancer-related deaths increased from 21% to 31% and 28% to 35%, respectively.
Non-CVD non-cancer NCD deaths among normal-weight people almost doubled from 21% to 37%. Significant increases in these deaths were also observed among overweight individuals from 20% to 34%, as well as obese individuals from 18% to 29%.
In obese individuals, neurological disease caused significantly more deaths, from nearly zero to 6%. Likewise, neurological disease caused more deaths in normal-weight and overweight individuals, with these rates rising from 2% and 4% to 9% and 11%, respectively.
Respiratory deaths doubled from 7% in both normal weight and overweight individuals to 14% and 11%, respectively. Respiratory-related deaths also rose among obese individuals from 4% to 7%.
Digestive tract-related mortality also rose from 3% to 6% for both normal weight and obese, but not overweight individuals.
Causes of death in females
In females, CVD deaths declined sharply in all categories from 43-44% in 2004 to 30% and 32% in normal weight and obese individuals in 2019, respectively. CVD deaths in overweight women also declined from 39% to 26% between 2004 and 2019, respectively.
Cancer deaths declined from 37% to 27% in overweight women and from 30% to 27% in normal-weight women while rising from 22% to 28% among obese women. Non-cancer non-CVD NCD deaths increased overall but doubled from 19% to 38% in overweight women.
Neurological deaths increased eight-fold among overweight women from 2% to 16% as compared to 1% to 13% for normal-weight women and 4% to 9% for obese women. Respiratory deaths among obese women doubled from 3% to 7%.
Conclusions
Despite the continued growth of obesity, improvements in treatment, risk factor management, and/or lifestyle changes appear to have offset or negated the impact of obesity as a risk factor for cardiovascular disease.”
Cancer has replaced CVD as the leading cause of mortality among men and overweight females. Neurological disease, mainly dementia, is also a leading cause of mortality, along with other non-cancer non-CVD NCDs. Neurological mortality rates were highest for overweight individuals, with obese and overweight individuals exhibiting the most significant proportionate increase.
Female life expectancy in England increased in the least deprived areas and declined in the most deprived areas. Male life expectancy increased overall, with insignificant increases observed in the most deprived areas. Thus, financial insecurity, like obesity-related CVD, is a determining factor in mortality.
Further screening, prevention, and treatment implementation for a broader set of diseases is necessary for continued mortality improvements.”
Future research using a larger sample and a more extended follow-up period is needed to ensure precise mortality estimations and rule out reverse causation.
Journal reference:
- Sophiea, M. K., Zaccardi, F., Cheng, Y. J., et al. (2024). Trends in all-cause and cause-specific mortality by BMI levels in England, 2004–2019: a population-based primary care records study. The Lancet. doi:10.1016/j.lanepe.2024.100986.