A UK Biobank study has found that genetics accounts for eight percent of the difference in people's feelings of tiredness and low energy.
The study analysed genetic information from 111,749 participants, who all indicated whether they felt tired or low in energy in the two weeks prior to the data collection.
The researchers found that small genetic contributions to self-reported tiredness overlapped with genetic contributions to a range of mental and physical health conditions, and with whether people smoke, or are carrying too much weight, and also to longevity.
It was the genetic susceptibility to some illnesses itself, not just the presence of these illnesses, that was associated with self-reports of tiredness. For example, people who were genetically prone to diabetes, but did not have the condition, were still more prone to tiredness. There was an overlap between tiredness and a general tendency to poor health.
'Being genetically predisposed to a range of mental and physical health complaints also predisposes people to report that they are more tired or lacking in energy,' said Saskia Hagenaars, a PhD student at the University of Edinburgh's Centre for Cognitive Ageing and Cognitive Epidemiology, who led the study.
Genetic factors accounted for 8.4 percent of people's differences in tiredness.
In the paper, the researchers refer to the Scottish term 'wabbit', which 'encompasses both peripheral fatigue, the muscle weakness after a long walk, and central fatigue, the reduced ability to initiate and/or sustain mental and physical activity, such as we might experience while having flu'.
'Some people report feeling generally more wabbit than others. Our results suggest that a small but detectable part of that variation is related to differences in people's genes. And the genes involved are associated with a range of health and personality factors,' said Dr Vincent Deary of Northumbria University Deary, co-author of the study, which was published in the journal Molecular Psychiatry.