Those who are obese in early to mid-life are at higher risk of developing dementia, while seniors appeared to be at reduced risk.
The research team, including Prof. Michael Goldacre of the University of Oxford in the UK, recently published their findings in the Postgraduate Medical Journal - a journal of The BMJ.
"Although data on different age groups have been published in different studies, previous studies have not looked at the age-related effect of obesity on the risk of dementia within a study of a single defined population covering all ages," say the researchers.
With this in mind, Prof. Goldacre and colleagues set out to assess whether the risk of later-life dementia among obese individuals in England is influenced by the age at which they are obese.
Dementia risk highest for obese individuals in early to mid-life
The team analyzed hospital records for the whole of England between 1999 and 2011.
From this, they identified 451,232 obese individuals, of which 57% were women. Their records were then assessed for any care received for dementia and any deaths from the condition.
Fast facts about obesity in the US
- More than a third of US adults (78.6 million) are obese
- Obesity is highest among adults aged 40-59
- Women with higher income are less likely to be obese than those with lower income.
Results of the analysis revealed that the risk of developing dementia among obese individuals was very much influenced by their age.
In detail, the team found that obese people aged 30-39 were 3.5 times more likely to develop dementia that non-obese individuals of the same age.
However, this increased risk reduced with age. Obese people in their 40s were 1.7 times more likely to develop dementia than non-obese individuals, those in their 50s had a 1.5 times higher dementia risk, while those in their 60s had a 1.4 times higher dementia risk.
Obese individuals in their 70s were no more or less likely to develop dementia, while those in their 80s were 22% less likely to develop the condition.
The researchers also found that obese people in their 30s were at increased risk for developing vascular dementia or Alzheimer's disease - the most common form of dementia. Those who were obese between the ages of 40 and 60 had a higher risk of vascular dementia, while those over the age of 60 had a reduced risk of Alzheimer's disease.
Protective effect of obesity in older age 'surprising'
When asked if the team was surprised by their results, Prof. Goldacre commented that they were when it came to the finding that obesity may actually protect older individuals against dementia.
"One possible explanation is simply that obese people who are not prone to obesity-related premature death - the 'survivors' - are indeed not at risk in old age. Another possibility is that, in people whose obesity may have genetic determinants, obesity may have certain survival benefits that are themselves associated with a lowered risk of dementia."
When it comes to increased dementia risk among obese individuals in their 30s and 40s, the researchers say this could be down to the fact that obesity is linked to cardiovascular problems and diabetes, which are linked to a higher risk of dementia themselves.
He noted, however, that the study findings are observational and are therefore unable to establish a causal link.
"But if the findings in the young are cause-and-effect - that obesity contributes to the development of dementia, either directly or via its association with a raised risk of circulatory disease - dementia becomes yet another hazard of obesity. So, if cause-and-effect, the findings add to the importance of dealing with the obesity epidemic."
The researchers say there are some limitations to the study. For example, they note that their research was not based on individuals who had been followed-up from the first recognition of obesity, but from hospital records reporting first admissions for obesity.
"The short time span of the dataset means that we have no way of knowing if people whose first admission for obesity at say, 70, actually were obese at say, 30, decades before the advent of linked hospital episode statistics data," they explain.
In addition, they say there is a possibility that the age effect reported in this study might be down to a birth cohort effect.
"It is possible that the difference between dementia risk in someone whose obesity was first recorded when aged 30 years and someone aged 70 years is attributable to their being born in very different generations," they add.
Medical News Today recently reported on a study published in The Lancet, which suggested overweight and obesity is linked to an increased risk of 10 common cancers.