There has been rather little research looking at time trends and the few that there have been are confined to health. However, there have now been something like 200 mainly cross-sectional studies of the relation between income distribution and health at different points in time in different settings. It is of course impossible that the two would appear related at successive points in time unless they changed together over time. If two things almost always appear together, then it is safe to assume that they move together. (The possibility that they remain in the same place can be discounted: we know that there have been very substantial changes in income distribution.)
The difficulty in tracking the links is the likelihood that long and differing lag periods are involved. We know for instance that health in middle and old age is strongly influenced by early life experience – as well as experience over the intervening years. Each age group would require different lag periods, and different causes of death take different amounts of time to develop. On top of that, comparable international data on income distribution has not been available for very long. In this situation it is impressive that studies have found relationships between changes in income inequality over time and changes in death rates.