Satisfaction with life and major depression share a genetic cause, researchers have reported.
The findings come from research on twins in Norway.
Researchers say this shows a strong genetic link between satisfaction with life and reduced risk of major depression, representing about 74% of the link between the two mental states.
The findings have been reported in the Journal of Affective Disorders.
The researchers say the findings suggest that people at risk of depression are unlikely to stave it off by indulging in activities that make them happy.
Researcher Ragnhild Bang Nes, from the division of Mental Health of the Norwegian Institute of Public Health, said: "The stable tendency to see the bright side of life is associated with lower risk of major depression because some genetic factors influence both conditions."
He explained: "The heritability figures mean that 72% of the individual differences in overall satisfaction, and 34% of the differences in depression, are caused by genes."
He added: "We found that depression and life satisfaction did not share as many environmental factors as genetic factors. This means that environmental factors of importance to life satisfaction (for example, activities and interventions that make you happy and content) only to a small extent protect against depression.
"Although our underlying disposition to life satisfaction and positivity appears to be relatively stable, small actions in our daily lives may provide temporary pleasures, and these are also important.
"How we spend our time is tremendously important for our happiness and well-being. It is therefore important to encourage and follow up on activities that make us happy."
Major depression and life satisfaction: A population-based twin study. Journal of Affective Disorders 2012 doi: http://dx.doi.org/10.1016/j.jad.2012.05.060
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