In India, rural and lower-caste older adults can expect fewer years with a healthy mind, mostly because they die sooner

India's population is aging fast: by 2050 the country is expected to have about 330 million people aged 60 or older. Living longer is only part of the story. What matters too is how many of those extra years are spent with a clear mind, free of dementia (memory and thinking problems serious enough to disrupt daily life) or its milder forerunner, mild cognitive impairment.

A team led from the Johns Hopkins Bloomberg School of Public Health estimated this "cognitively healthy life expectancy" for India as a whole and for groups that differ in where they live and in caste, the hereditary social ranking that still shapes access to schooling, work and health care in India even though caste discrimination was outlawed in 1949.

What they did

• Memory and thinking: 4,096 people aged 60 and over, part of the nationally representative Longitudinal Aging Study in India, took a detailed set of cognitive tests designed to work across many languages and for people with little schooling, and a relative or friend was interviewed about changes in their thinking and daily functioning. From this, each person was classed as cognitively healthy, mildly impaired or having dementia.
• Deaths: national death rates by age, sex and rural or urban residence came from India's official life tables for 2015–2019. Death rates by caste came from household reports in a 2015–16 national health survey.
• Putting them together: a standard method (the Sullivan method) splits the years a person can expect to live from a given age into years with and without impairment. A second step worked out whether gaps between groups were due to different death rates or to different rates of impairment.

The comparison groups were women and men; rural and urban residents; and three social groups: Scheduled Castes and Scheduled Tribes, the most disadvantaged; "Other Backward Classes"; and high castes.

What they found

• About a quarter of people 60+ had some impairment: 17.4% had mild cognitive impairment and 7.4% dementia.
• Women and men were close. At 60, women could expect 14.3 cognitively healthy years and men 13.5. Both would spend roughly a quarter of their remaining life with some impairment; men more of it with mild impairment, women more of it with dementia.
• City versus village. Urban women could expect 15.8 healthy years from 60, about 2.2 more than rural women. Urban men could expect 15.3, against 12.2 for rural men, a gap of about 3.1 years. Urban men spent 80% of their remaining life cognitively healthy, rural men 72%.
• Caste. High-caste women could expect 15.3 cognitively healthy years from 60, against 11.6 for women from Scheduled Castes and Tribes. For men the gap was about 5.3 years.
• Mostly a matter of survival. For most comparisons, earlier death in the disadvantaged group explained more of the gap than higher rates of impairment. For example, of the 5.3-year caste gap among men, about 3 years came from death rates and 2.3 from impairment.

What to keep in mind

• A snapshot turned into a forecast. The method combines current death rates with a one-time measurement of impairment and assumes these stay stable; it cannot follow people as they move from healthy to impaired. The authors note this design can't tell apart the possible reasons for the differences between women and men.
• Impairment is probably undercounted. Compared with clinicians' ratings, the classification rarely labels healthy people as impaired but misses some real cases.
• Imperfect death data. Caste-specific death rates come from what households reported, which is prone to memory errors; the authors argue this probably makes the caste gaps they report conservative.
• Small numbers in some groups. Age bands had to be wide (60–69 and 70+), and for the rural/urban and caste comparisons impairment was counted as a single category; some groups had very few of the oldest people.
• Descriptive, not causal. The study describes differences between groups. It doesn't show what lies behind them, though the authors point to schooling, nutrition, work, air pollution and access to care as likely contributors.

Why it matters

The number of older people living with dementia in India is set to grow. This study suggests that, in India, a large part of the inequality in years lived with a healthy mind comes from disadvantaged people dying earlier, not only from higher rates of memory problems. The authors conclude that tackling excess deaths in rural and lower-caste communities, through better access to care and control of chronic diseases, should go hand in hand with efforts to detect and reduce dementia risk.