If dementia is all you are worried about, a study of British public servants suggests that you could even double the pork and fish and chips. In JAMA on March 12, researchers led by Tasnime Akbaraly at the Montpellier University in France reported that middle-aged eating habits among people in the Whitehall cohort had no influence on their risk of dementia until 25 years later. A healthier diet has reduced mortality, suggesting at least some benefits from vegetables, fruits and healthy fats.
- The middle-aged diet did not correlate the risk of dementia in 25 years.
- The diet deteriorated in the decade before the onset of dementia.
- A healthier diet protected against dementia in people who had cardiovascular disease at baseline.
Most commentators were quick to note that, despite its size, length and careful analysis, this observational study cannot provide the final word on the relationship between diet and dementia. "At first glance, the results seem surprising and liberating for those interested enough to limit their diet to healthier choices," commented Gregory Cole of the University of California, Los Angeles. "But before giving up seemingly healthy diets, readers should consider some of the important limitations of the study." For Cole, these include a predominantly male cohort, no data for ApoE4 carriers and missing dietary details that may have attracted a cognitive benefit.
Despite numerous previous studies, the relationship between diet and cognitive decline is anything but clear. In intervention studies, most diets, with the exception of the Mediterranean, failed to slow down cognitive decline (Andrieu et al., 2017, Marseglia et al., 2018, Nov 2017, Valls-Pedret et al., 2015 ). Some observational studies have reported cognitive benefits of some diets; however, this type of study is full of confounding factors and most follow people for less than 10 years (van de Rest et al., 2015; Cao et al., 2016; news in August 2009).
Researchers sought to address these problems by tapping the data from one of the longest-standing observational studies of both dietary and cognitive data. The Whitehall II study enrolled 8,225 British state officials between 1991 and 1993, when their average age was 50 years. Two thirds were men. They underwent clinical evaluations approximately every five years, for a total of 24.8 years on average. At three visits, in 1991-1993, 1997-1999 and 2002-2004, they completed food frequency questionnaires, from which the researchers generated an AHEI score (Alternative Healthy Eating Index). The index ranges from zero to 110 points and was developed as part of the nurse health study, which reported higher scores related to a lower incidence of chronic diseases such as cardiovascular disease and cancer (Chiuve et al. , 2012). On the AHEI, more points are given for greater intake of foods considered healthy, including whole fruits and vegetables, whole grains, nuts and legumes, and long-chain omega-3 fatty acids. Foods considered unhealthy, such as red and processed meat, trans fats and sodium, have a lower score. The researchers modified their questionnaire to reflect foods commonly consumed in England. At baseline, participants had an average AHEI score of 52.
The primary outcome was the incidence of dementia ascertained from electronic health records. Cognitive decline, assessed by the change in global cognitive scores for an average of 18 years, was a secondary outcome. Researchers controlled numerous socio-demographic factors, including marital status, employment, education and ethnicity, as well as behavioral and health factors, such as smoking, alcohol consumption, physical activity, diabetes, cardiovascular disease and ApoE4 genotype.
Among the 6,961 participants with sufficient dietary and cognitive data, 344 cases of dementia were reported in 2017, with 75% of those registered after 2010. The researchers found no correlation between the AHEI therapist at any risk of visitation and dementia during the study. They also found no association between tertiles and cognitive decline. However, people with the highest tertile had a lower risk of mortality by 2017, suggesting a correlation between this dietary index and health in this cohort. Since the researchers did not report whether the highest AHEI scores are correlated with the reduced risk of diet-related diseases, such as diabetes, stroke or cardiovascular disease, it is not clear to what extent the score reflects the quality of the diet.
To address the possibility that the AHEI score did not accurately capture participants' eating habits, the researchers also used their answers to the food questionnaire to generate dietary patterns in the aftermath. In a major component analysis, which identifies dominant patterns within complex datasets, two models have emerged: a healthy diet, which included fruits, vegetables and fish; and a western-style diet, which was heavy with fried foods, processed red meat, pies, chocolate, high-fat dairy products and refined grains. However, similar to the AHEI, the degree of adherence of the participants to both patterns was not related to the risk of dementia. C & # 39; was an exception. In a post hoc analysis, the researchers found a lower risk of dementia among 41 people with a history of cardiovascular disease who reportedly adhered to a healthy eating pattern at the time of the 2002-2004 visit. People without a history of cardiovascular disease and / or a healthy diet only in previous years have not been protected.
Researchers have also explored the possibility that people who developed dementia could veer towards a less healthy diet. To solve this problem, the researchers compared the trajectories of AHEI scores in people who later developed dementia with those who did not. Their scores were head-to-head for the first nine years of the study, but at age 10, AHEI scores started to drop slightly in people who developed dementia. This suggests that a change in diet quality is a feature of preclinical dementia, the researchers wrote. These findings concern, noted Nikolaos Scarmeas of Columbia University in New York, as they support the idea of reverse causality, which has long been suspected of confusing observational studies.
While most commentators considered the study important, they noted caveats that precluded definitive conclusions. Karen Murphy of the University of South Australia in Adelaide believes the AHEI may not have captured some critical components of a healthy diet. For example, were noshing fruit eaters on dark berries, which are rich in antioxidants and flavonoids, or bananas, which are not? Were they chocolate eaters who consumed dark chocolate rich in antioxidants, or stuffed themselves with the sweetened milk variety? Cole agreed that the devil could be in the details. "Fish consumption can be protective, but it is not clear what it means in the UK, with its tradition of fried fish and chips," he wrote. In the cohort study of the women's health initiative, fish reduced the risk of heart failure, while fried fish increased it (Belin et al., 2011).
Cole added that people who developed dementia had more cardiovascular risk factors. "This suggests that the risk of dementia in the study is substantially driven by cardiovascular risk factors, but those with healthier diets were not protected from cardiovascular disease or dementia. On the contrary, some important studies on interventions on the Mediterranean diet have shown protection. very clear against the risk of CVD, "he wrote. This suggests that even those in the highest AHEI trio may not have had healthy diets.
Cole also noted that while the researchers adjusted to the ApoE4 state, they did not provide data broken down by genotype, which may have revealed correlations. In other studies, ApoE4 carriers have benefited more from dietary interventions and other lifestyles than non-carriers. "This study population is 69.1 percent male, while the risk of dementia is substantially higher in women, particularly women with ApoE4," he added.
Claire McEvoy of Queen's University of Belfast complained of a lack of consistency between the food indices used in the studies. "Defining a food index specifically aimed at improving cognitive performance would be desirable for future studies so that the results can be compared more easily," he noted. Two previous observational studies found no association between AHEI scores and dementia (Haring et al., 2016, Richard et al., 2018).
Just this month, the CARDIA study reported that, among a racially diverse population of participants, greater adherence to the Mediterranean diet or A Priori Diet Quality Score (APDQS) in adulthood associated with greater cognitive function in middle age (McEvoy et al., 2019). The numerous differences between the studies of McEvoy and Whitehall – including the diversity and age of populations, the evaluation of diet and the measurement of cognition – preclude a direct comparison between their results, McEvoy wrote. Another important difference between the studies is that CARDIA was racially different. "Different ethnic groups can suggest different genetic susceptibilities and different pathologies related to cognition and therefore different responses to nutritional factors," he wrote.
Michelle Luciano, University of Edinburgh, agreed that the Whitehall cohort, consisting of predominantly white London employees, does not reflect a larger population. "Further studies must include a more diverse demographic population that could have a wider range of eating habits," he wrote. "Other large prospective population studies are needed to resolve the debate on the possibility that a healthy eating style can protect against dementia." – Jessica Shugart
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