Isn't this obvious.

Here is an excerpt from a BBC.com article: 

Unhappy children 'end up unwell'

Unhappy children are more likely to grow up to become adults who are permanently sick or disabled, a UK study has suggested.

The King's College London-led research looked at over 7,100 people born between 1950 and 1955. Researchers found those described as "miserable" or "unhappy" by teachers were five times more likely to be off work through ill-health in middle age. They said these children were also likely to be more prone to depression. The study, published in the British Journal of Psychiatry, involved thousands of children who grew up in Aberdeen in the 1950s. Teachers were asked about their temperament and school attendance.

Researchers recently tracked down many of the participants - now in middle age - to ask them about their employment status. Some 392 reported they were unable to work because of permanent disability or ill-health - 5.5% of the total questioned. This could have included those retired through illness and those on incapacity benefit. A quarter of those whose teachers had reported them as "often appearing miserable, unhappy, tearful or distressed" were permanently sick or disabled.

A quarter of those who complained of aches and pain were also off sick through ill-health.

But those who were off school because of poor physical health were no more likely to end up as adults off work sick.