In a recent study published in the Journal of the American Medical Association, scientists report that people with a high genetic risk of developing dementia who made healthy lifestyle choices had a lower risk of developing dementia than people with a high genetic risk who made unhealthy lifestyle choices.
Researchers retrospectively studied a group of people of European descent aged 60 years and older who, at the start of the study, were not cognitively impaired and did not have dementia. They constructed two types of risk scores for each of the over 196,000 study participants: a genetic risk score, and a healthy lifestyle score. Since previous research has shown that multiple genes influence the risk of developing Alzheimer’s disease and dementia, the genetic risk score takes into account multiple versions of various gene mutations. The healthy lifestyle score considered known dementia risk factors: whether individuals smoked tobacco or not, whether they engaged in regular physical activity, ate a healthy diet, and consumed alcohol in moderation. Dementia was determined from inpatient hospital records and death records. Statistical models were used to estimate associations between genetic risk, lifestyle risk, and the combination of both of these risks on the risk of developing dementia.
THE FINDINGS
The effect of genetic risk on dementia risk
As genetic risk category changed from low to intermediate to high genetic risk, scientists observed an increase in the risk of developing dementia. People with intermediate genetic risk had a 1.3-fold increase in the risk of developing dementia, compared to the low-risk group. People at a high genetic risk of developing dementia saw an almost 2-fold greater risk of developing dementia relative to the low genetic risk group. Among the people who had a low genetic risk, about 1 in 150 people developed dementia. For people in the high genetic risk group, the risk of developing dementia increased to about 1 in 80 people.
The effect of lifestyle on dementia risk
As lifestyle categories changed from favourable to intermediate to unfavourable, the researchers reported an increased risk of developing dementia. Study participants with intermediate lifestyle scores had about a 1.2-fold increase in the risk of developing dementia, compared to people with favourable lifestyle scores. Participants with unfavourable lifestyle scores had about a 1.4-fold increase in the risk of developing dementia, relative to people with favourable lifestyle scores. Among the people who had favourable lifestyle scores, about 1 in 120 people had dementia. For people in the unfavourable lifestyle category, the risk of developing dementia increased to about 1 in 85.
The effects of both genetic risk and lifestyle on dementia risk
As genetic risk increased and as lifestyle choices became unfavourable, the risk of developing dementia increased. For all genetic risk groups, a favourable lifestyle was associated with a lower risk of developing dementia than an unfavourable lifestyle. Among people with low genetic risk, those with unfavourable lifestyle scores had about a 1.5-fold increase in the risk of developing dementia relative to those with favourable lifestyle scores.
Among study participants with intermediate genetic risk, people with favourable lifestyle scores had about a 1.4-fold increase in the risk of developing dementia compared with people with low genetic risk and favourable lifestyle scores. For people with intermediate genetic risk and unfavourable lifestyle scores, the risk of developing dementia increased to about 1.7-fold relative to people with low genetic risk and favourable lifestyle.
Finally, for those people who had a high genetic risk, people with favourable lifestyle scores had about a 2-fold increase in the risk of developing dementia compared to people who had low genetic risk and favourable lifestyle score
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People with high genetic risk and an unfavourable lifestyle had an almost 3-fold increase in the risk of developing dementia relative to people with low genetic risk and favourable lifestyle score. Amoung study participants who had a low genetic risk and favourable lifestyle score, about 1 in 180 developed dementia. For people with high genetic risk and unfavourable lifestyle score, the risk of developing dementia rose to about 1 in 55 people.
SUMMARY OF FINDINGS
Scientists found that in this population of people who did not initially have cognitive impairments or dementia, both having a high genetic risk score and having a low healthy lifestyle score were each associated with a higher risk of developing dementia. For study participants who were in the high genetic risk category, having a favourable lifestyle score offset the increased genetic risk – these participants had a lower risk of developing dementia than those with an unfavourable lifestyle score.
Both having a high genetic risk score and having a low healthy lifestyle score were each associated with a higher risk of developing dementia.
RELEVANCE OF THE STUDY
While it was known that certain genetic factors can increase the risk of developing dementia, this study addresses a gap in the literature because it was not known the extent to which lifestyle choices can offset this increased risk. Also, the study further advances our understanding because to the authors’ knowledge, there had been no previous studies that examined the combined effects of lifestyle risk factors and multiple genetic risk factors on the risk of developing dementia. A separate study investigated the combined effects of lifestyle and genetic risk on the risk of having a stroke, among other cardiovascular diseases. The percentages of people who were at risk of having a stroke reported in that study were similar to the percentages reported in this study on the risk of developing dementia.