Lifespan disparity ( \(e^{\dagger}_0\) ) varies for similar values of life expectancy ( \(\:{e}_{0}^{}\) ) owing to changes in the shares of premature and old-age mortality about threshold age on one hand, and in the composition of causes of death on the other. Decomposition analyses of \(\:e_0^+\) for 24 causes of death using mortality rates from the 2021 Global Burden of Disease (GBD) study were used to assess its age-cause-specific contributions in the progression of \(e^{\dagger}_0\) during 1990–2019. The results reveal that \(e^{\dagger}_0\) values for men and women declined from 17.7 to 17.4 years in 1990–1994 to 13.2 and 12.9 years, respectively, in 2015-20l9. This decline in \(e^{\dagger}_0\) was mainly due to four diseases: respiratory infections, enteric infections, neonatal disorders, and other infectious diseases in infants, children, and childbearing age groups. On other hand, the unfavourable roles of cardiovascular and chronic respiratory diseases in the passive decline in \(e^{\dagger}_0\) have been attributed to the low threshold age. Hence, the share of premature mortality has not been sufficient for the progressive decline in \(e^{\dagger}_0\) in India, when compared with HICs/UMICs and LMICs with \(\:{e}_{0}^{}\) in range of ± 2. Thus, the changes in \(e^{\dagger}_0\) shaped by a few age groups and selected causes of death would progress differently compared to when contributed by many age groups and causes of death. Our results suggest India should focus on programs and policies averting deaths among older adults caused by CVDs and CRDs, which may shift the threshold age upward for a leap in mortality advancement.
