By Shreeya Nanda, Senior medwireNews Reporter
A meta-analysis has identified the key modifiable factors associated with an increased or decreased risk of Alzheimer’s disease (AD).
The findings show that around two-thirds of AD incidences could be attributable to such factors, including dietary and biochemical exposures, psychological conditions, pre-existing diseases and lifestyle factors.
Therefore, “effective interventions” targeting them “may decrease new incidences of AD”, the researchers say.
Of 93 factors identified from 323 longitudinal cohort or retrospective case–cohort studies published between 1968 and 2014, 13 were associated with an increased (between one- and twofold) AD risk while 23 were linked to a reduced risk.
The highest quality evidence available showed that ever use of oestrogen, current statin use, as well as the use of antihypertensive medications and non-steroidal anti-inflammatory drugs protected against the development of AD, as did high folate, vitamin C and E intake, and coffee consumption. By contrast, depression and high serum levels of total homocysteine increased the risk of developing AD.
The study authors found that the role of pre-existing disease in relation to AD risk was complex – diastolic blood pressure less than 70 mmHg, systolic blood pressure of 160 mmHg and higher, carotid atherosclerosis, Type 2 diabetes in Asian individuals and frailty increased the risk. But a history of arthritis, cancer, heart disease or metabolic disease reduced the risk.
Lifestyle factors were similarly complex, with high body mass index (BMI) in midlife and late life associated with an increased and decreased risk, respectively. Low BMI (<30 kg/m2) was associated with an increased risk, as was low educational attainment. By contrast, cognitive activity, light-to-moderate alcohol consumption and stress were found to be protective against AD development.
Although smoking was not associated with AD risk in the primary analysis, subgroup analysis revealed significant but opposing associations of current smoking in Western and Asian populations – protective in the former, but associated with an increased risk in the latter (albeit with weaker evidence than for Western populations). And after adjusting for heterogeneity, heavy smoking (between 55.5 and 156.0 pack–years) was identified as a risk factor for developing AD.
Researcher Jin-Tai Yu, from the University of California San Francisco in the USA, and co-workers used global prevalence data available for nine of the 13 risk factors to calculate the population attributable risk, which ranged from 0.18% for frailty to 24.50% for current smoking in Asian populations.
Taken together, these nine potentially modifiable risk factors account for approximately two-thirds of global AD cases, they say in the Journal of Neurology, Neurosurgery & Psychiatry.
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