Is there any link between low levels of mental functioning and poor health? A study shows that the same genes which influence people's health also shape how effectively they think.

The scientists found that genes associated with diseases, including Alzheimer's, schizophrenia and autism, also have an impact on some cognitive functions.

"In addition to there being shared genetic influences between cognitive skills and some physical and mental health states, the study also found that cognitive skills share genetic influences with brain size, body shape and educational attainments," said lead research professor Ian Deary from the University of Edinburgh.

The study, published in Molecular Psychiatry, was led by the University of Edinburgh that analysed data from around 100,000 people held in the UK Biobank.

To test the findings, researchers gathered data from previous genetic studies of other mental and physical health factors -- such as Alzheimer's disease, schizophrenia and autism.

To come to the conclusion, the national resource of health data helped researchers discover why some people develop particular diseases and others do not.

The researchers compared each person's mental test data with their genome-organism's complete set of DNA and found that some traits linked to disease and thinking skills shared the same genetic influences.

"The study supports an existing theory which says that those with better overall health are likely to have higher levels of intelligence," said another researcher, Saskia Hagenaars.