Obesity is linked to a higher risk of dementia in later life, according to a new study.

The study has found that the age at which a person is obese seems to be a major factor in the risk of developing dementia at a later stage in life, with the findings indicating a tripling in risk for people in their 30s.

The researchers used data from hospital records in England for the period 1999-2011, in which obesity had been recorded in patients who were then checked by the researchers for any subsequent care for, or death from, dementia.

During the study period, 451,232 of those admitted to hospital were diagnosed with obesity, and 43% of these were men.

The study showed a growing decrease in overall risk of hospital admission for dementia the older a person was when obesity was first recorded, irrespective of their gender.

For people aged 30-39, the relative risk of developing dementia was 3.5 times higher than in those of the same age who were not obese.

People in their 70s with obesity were neither at greater or lower risk of developing dementia, while those in their 80s were 22% less likely to develop the disease, the findings indicated.

The study mirrored findings from smaller studies which reported an increased risk of dementia in young people who are obese, but a reduced risk in older people who are obese.

The researchers believe the reason for the greater risk in early to mid-life may be that that heavier weight is associated with diabetes and cardiovascular disease risks factors, which are themselves linked to a greater risk of dementia.

The researchers believe the findings indicate if people can hold off significant weight gain until at least into their 60s, or survive long enough with obesity, they may have a lower risk of developing dementia when they get older.

The study is published in the Postgraduate Medical Journal.