Election to head of government is associated with an increased risk of death compared with runner-up candidates, finds a study in the Christmas issue of The BMJ.

However, a second study finds that in the UK, mortality among members of Parliament (MPs) and members of the House of Lords (Lords) was up to 37% lower than that of the general population over the past 65 years.

In the first study, a team of US researchers set out to test the theory that politicians elected to head of government may experience accelerated aging and premature death due to stress of leadership and political life.

They compared survival of 279 nationally elected leaders from 17 countries with 261 unelected candidates who never served in office, from 1722 to 2015.

They then measured the number of years alive after each candidate's last election, relative to what would be expected for an average individual of the same age and sex as the candidate during the year of the election.

After adjusting for life expectancy at time of last election, elected leaders lived 2.7 fewer years and had a 23% increased risk of death than runners-up.

The researchers point out some study limitations, but conclude that "heads of government had substantially accelerated mortality compared to runner-up candidates," and suggest that "elected leaders may indeed age more quickly."

In the second study, UK researchers examined mortality in almost 5,000 members of the two UK Houses of Parliament compared with the general population over a 65-year period, from 1945-2011.

They compared the observed mortality in members with the expected mortality of the general population, matched to the same sex or age of the member in the year of entry to parliament.

They found that the death rates of MPs were 28% lower than those of the general population, while Lords experienced 37% lower relative mortality.

Furthermore, the mortality gap between MPs and the general population widened significantly at least until 1999, suggesting that over this period MPs may have become less representative of the population they serve, say the authors.

Mortality among Conservative MPs was lower than in MPs from other political parties, which may reflect underlying differences in social background, particularly in education, they add.

The results also show that MPs first elected at age 60 or more had lower relative mortality than MPs who were elected when younger, while long serving MPs went on to live longer lives than other MPs.

The authors conclude that "social inequalities are alive and well in UK parliamentarians, and at least in terms of mortality, MPs are likely to have never had it so good."