Very high or low BMI levels can kill you, study suggests

New research led by the London School of Hygiene and Tropical Medicine suggests both high and low body mass index (BMI) levels are associated with an increased risk of death.

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"BMI is a key indicator of health. We know that BMI is linked to the risk of dying overall, but surprisingly little research has been conducted on the links to deaths from specific causes," study author Krishnan Bhaskaran said in a statement. "We have filled this knowledge gap to help researchers, patients and doctors better understand how underweight and excess weight might be associated with diseases such as cancer, respiratory disease and liver disease."

The study, recently published in the journal Lancet Diabetes and Endocrinology, is a one-of-a-kind analysis involving anonymous data on 3.6 million people and 357,512 deaths. The data covers about 9 percent of the United Kingdom's population.

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After adjusting for age, sex, drug use and socioeconomic status, researchers found that individuals considered obese (those with a BMI of 30 or more) were associated with an increased risk of both heart disease and cancer, two major causes of death. High BMI was also linked to respiratory disease, liver and kidney conditions. Obesity, according to the study, reduced life expectancy by 4.2 years in men and 3.5 years in women.

Additionally, being underweight (BMI under 21) was associated with an increased risk of heart disease, respiratory disease, Alzheimer’s, dementia and suicide.

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Bhaskaran and his team found that maintaining a BMI between 21-25 kg/m2 is associated with the lowest risk of dying from cancer and heart disease, and lower levels of morbidity overall.

The authors pointed out possible limitations, such as the lack of information regarding patient diet and physical activity, but hope their findings help public health workers better understand how underweight and excess weight may influence multiple aspects of health.

Read the full study at thelancet.com.