Midlife dietary habits were not tied to dementia incidence over a 20-year period, a prospective study in Sweden showed.
Adhering to conventional dietary recommendations or to a modified Mediterranean diet was not linked with lower incidence of all-cause dementia, Alzheimer’s disease dementia, vascular dementia, or amyloid pathology, reported Isabelle Glans, MD, of Lund University in Sweden, and colleagues.
“The study does not exclude a possible association between diet quality and subsequent development of dementia,” they wrote in Neurology.
“However, the present Swedish dietary recommendations, which are in line with those in the U.K. and U.S., or according to the Mediterranean dietary pattern, could not be confirmed to be associated with prevention of dementia,” the researchers added.
It’s “critically important to better understand the links between diet and nutrition and dementia risk,” observed Heather Snyder, PhD, vice president of medical and scientific relations at the Alzheimer’s Association in Chicago, who wasn’t involved with the study.
“To get there, the connections between diet and dementia risk must be examined in multiple studies across multiple populations and even multiple countries,” Snyder told MedPage Today.
“These new results represent one study and should be considered in the bigger landscape of the ongoing work,” she emphasized. “This is an observational study that can find an association between factors, but does not prove causation. For that, we need an intervention study. Fortunately, there are studies today that are testing dietary and nutrition-related interventions.”
“Beyond that, existing data suggest that there is synergy between different risk-reduction strategies and these strategies should be considered in combination, not one at a time,” Snyder pointed out. For example, the 2-year U.S. POINTER trial is evaluating whether lifestyle interventions that target multiple risk factors can benefit people with a higher risk of cognitive decline.
The Swedish study isn’t the first to suggest diet and dementia are not related. “The findings are overall in line with previous long-term studies addressing this topic,” noted Nils Peters, MD, of the University of Basel in Switzerland, and Benedetta Nacmias, PhD, of the University of Florence in Italy, in an accompanying editorial.
“Diet as a singular factor may not have a strong enough effect on cognition, but is more likely to be considered as one factor embedded with various others, the sum of which may influence the course of cognitive function (diet, regular exercise, vascular risk factor control, avoiding cigarette smoking, drinking alcohol in moderation, etc.),” they wrote. “Thus, diet should rather be regarded as one part of a multidomain intervention with respect to cognitive performance.”
Glans and colleagues followed 28,025 people in the Swedish population-based Malmö Diet and Cancer Study who were dementia-free at baseline and who had baseline exams from 1991-1996. Mean baseline age was 58 and 61% were women.
The researchers used a 7-day food diary, a detailed food frequency questionnaire, and a 45-60 minute interview to evaluate dietary habits at baseline.
Swedish dietary guidelines scores, designed to reflect a healthy diet based on Swedish nutritional guidelines, were calculated based on average daily food intake. Eating patterns also were assessed by adherence to a modified Mediterranean diet that focused on a high intake of vegetables, legumes, fruits, fish, and healthy fats and a low intake of dairy products, meat, and saturated fatty acids.
Dementia diagnoses were determined by memory clinic physicians. A subpopulation of 738 participants had analyses of cerebrospinal fluid (CSF) levels of amyloid-beta 42 when they were referred to the Skåne University Hospital in Malmö memory clinic after developing clinical signs of cognitive impairment.
The primary outcome was progression to all-cause dementia. Secondary outcomes were progression to Alzheimer’s dementia and vascular dementia. Over a median follow-up of 19.8 years, 1,943 people (6.9%) were diagnosed with all-cause dementia.
A comparison of worst-versus-best adherence to conventional dietary recommendations showed no difference in risk of all-cause dementia (HR 0.93, 95% CI 0.81-1.08), Alzheimer’s dementia (HR 1.03, 0.85-1.23) or vascular dementia (HR 0.93, 95% 0.69-1.26).
Likewise, worst-versus-best adherence to a modified Mediterranean diet did not lower the risk of developing all-cause dementia (HR 0.93, 95% 0.75-1.15), Alzheimer’s dementia (HR 0.90, 95% 0.68-1.19) or vascular dementia (HR 1.00, 95% 0.65-1.55).
In sensitivity analyses, results were similar when excluding people who developed dementia within 5 years or people with diabetes. Neither conventional diet recommendations nor a modified Mediterranean diet had a significant association with abnormal CSF amyloid-beta markers.
The results come with several caveats, Glans and colleagues noted. Dietary data were collected only at baseline and dietary habits may have changed during the follow-up period. In addition, participants with CSF samples were not randomized, but were recruited based on clinical indications.
“Randomized controlled trials are needed to provide additional evidence regarding the potential role of diet in relation to Alzheimer’s disease pathology,” they wrote.
The study was funded by the Swedish Research Council, the Knut and Alice Wallenberg Foundation, the Marianne and Marcus Wallenberg Foundation, the Strategic Research Area MultiPark at Lund University, the Swedish Alzheimer Foundation, the Swedish Brain Foundation, the Parkinson Foundation of Sweden, the Konung Gustaf V:s och Drottning Victorias Frimurarestiftelse, the Skåne University Hospital Foundation, Regionalt Forskningsstöd, and the Swedish federal government.
Glans dislcosed no relationships with industry. Co-authors disclosed relationships with F. Hoffmann-La Roche, Biogen, Geras Solutions, AVID Radiopharmaceuticals, Eli Lilly, Eisai, GE Healthcare, Pfizer, Genentech, Siemens, Alzpath, and Cerveau.
Peters and Nacmias disclosed no relationships with industry.