BMI in older adults: why interpretation requires care
Learn how age-related changes in muscle and body composition can make BMI less informative in older adults.
The mathematical BMI formula does not change with age, and standard adult categories are often reported for everyone aged 20 and older. Interpretation, however, becomes more nuanced later in life.
Ageing can involve loss of muscle and changes in fat distribution. Two people with the same BMI may therefore have very different strength, mobility and body composition. A value in the standard healthy range can coexist with low muscle mass, while modestly higher BMI may not tell the full story either.
Unintentional weight loss deserves particular attention. It may accompany inadequate intake, dental or swallowing difficulties, medication effects, illness or frailty. Useful complementary information includes weight history, waist measurement, strength, walking ability, appetite and clinical or dietetic assessment.
The BMI calculator can supply a consistent reference number, but it should not be the only basis for a weight goal in an older adult. Seek professional review for rapid loss, weakness, repeated falls, reduced appetite or difficulty managing meals.