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Meta-analysis highlights modifiable risk factors for Alzheimer's disease

In a meta-analysis of 323 studies, researchers identified medical, dietary, biochemical, psychological and lifestyle factors associated with increased and decreased risk for Alzheimer’s disease.

“Large amounts of literatures with inconsistent conclusions have been published to investigate potentially modifiable risk factors of [Alzheimer’s disease], confusing our knowledge about this field. Therefore, we have carried out the most extensive and comprehensive systematic review and meta-analysis to date, which employs a full-scale search of observational studies to calculate effect sizes of various modifiable risk factors for [Alzheimer’s disease],” researchers from Qingdao University in Qingdao, China, wrote.

Researchers reviewed 323 prospective cohort studies or retrospective case-control studies that assessed 93 risk factors for Alzheimer’s disease and dementia.

Based on a pooled study population of more than 5,000 participants, researchers found grade I evidence that four medical exposures — estrogen, statins, antihypertensive medications and non-steroidal anti-inflammatory drugs — and four dietary exposures — folate, vitamins E and C, and coffee — had protective effects on Alzheimer’s disease risk.

“We found grade I evidence showing that one biochemical exposure (hyperhomocysteine) and one psychological condition (depression) significantly increased the risk of developing [Alzheimer’s disease],” the researchers wrote.

Complex roles of pre-existing disease, including frailty, carotid atherosclerosis, hypertension, low diastolic blood pressure and type 2 diabetes among Asian individuals were associated with increased risk for Alzheimer’s disease, while history of arthritis, heart disease, metabolic syndrome and cancer were associated with decreased risk.

Researchers also found grade I evidence that lifestyle factors including low education, high body mass index (BMI) in mid-life and low BMI were associated with an increased risk for Alzheimer’s disease. Cognitive activity, current smoking among Western populations, light-to-moderate drinking, stress and high BMI in late life were associated with a decreased risk for Alzheimer’s disease.

Researchers found no evidence of significant associations between occupational exposures and Alzheimer’s disease risk.

“The current meta-analysis emphasized the heterogeneity of modifiable risk factors of [Alzheimer’s disease] and the complexity of its etiology, and indicated that the effective interventions in diet, medications, biochemical exposures, psychological condition, pre-existing disease and lifestyle may be promising options for preventative strategies. Further good-quality cohort studies and randomized controlled trials targeting these elements are necessary,” the researchers concluded. – by Amanda Oldt

Disclosure: The researchers report no relevant financial disclosures.

Editor’s Note: On Aug. 25, we corrected language in the fifth, sixth and seventh paragraphs to more accurately reflect correlates of increased and decreased risk for Alzheimer’s disease. The Editors regret this error.