The more components of metabolic syndrome a person has in midlife seems to raise their risk of dementia, although that relationship seems to go away after age 70, a post hoc analysis of data from a major European cohort study has found.
A team of European researchers reported online in the journal Diabetes Care that the follow-up of the Whitehall II cohort study, a study of more than 10,000 civil servants in London that was established in the late 1980s, also found that cardiovascular disease (CVD) may only partially contribute to the risk of dementia in study participants.
They found that each additional metabolic syndrome component before age 60 years was linked to a 13% rise in the risk of dementia (hazard ratio, 1.13; 95% confidence interval [CI], 1.05-1.23) and, from age 60 to 70, the risk rose 8% (HR, 1.08; 95% CI, 1.00-1.16). However, in people aged 70 years and older, the relationship wasn’t statistically significant (HR, 1.04; 95% CI, 0.96-1.13]).
The study used “the latest harmonized definition” of metabolic syndrome; that is, participants were classified as having metabolic syndrome if they had three or more of the five components. As lead author Marcos D. Machado-Fragua, PhD, noted in an email interview, those components are abdominal obesity, high triglycerides, low HDL cholesterol levels, high blood pressure, and high fasting glucose.
“Our research question was on the association between metabolic syndrome and late-life dementia. We found that the presence of one metabolic syndrome component and the presence of metabolic risk before age 60, but not after, is associated with higher risk of dementia,” said Machado-Fragua, a post-doctoral researcher at the French Institute for Health and Medical Research in Paris.
The study cohort consisted of 10,308 London-based civil servants aged 35-55 years. Every 4-5 years after enrollment, from 1991 through 2016, they completed a questionnaire and had a clinical examination. The U.K. National Health Service electronic health record system tracked outcomes for all but 10 participants through March 2019.
The study identified the individual metabolic syndrome components that posed the highest risk for dementia in these three age groups:
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Age < 60 years: elevated waist circumference (HR 1.39 [95% CI 1.07, 1.81]), low HDL-C, (HR 1.30 [95% CI 1.02, 1.66]), and elevated blood pressure (HR 1.34 [95% CI 1.09, 1.63]).
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Age 60-70 years: low HDL-C (HR 1.26 [95% CI 1.02, 1.57]) and elevated fasting glucose (HR 1.40 [95% CI 1.12, 1.74]).
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Age >70 years: elevated fasting glucose (HR 1.38 [95% CI 1.07, 1.79]).
The study found that the dementia risk was significantly high in study participants under age 60 who had at least one (HR 1.99 [95% CI 1.08, 3.66]) or two (HR 1.69 [95% CI 1.12, 2.56]) metabolic syndrome components even when they didn’t have CVD.
“The present study adds to the understanding of the association between metabolic syndrome and dementia due to three novel features,” Machado-Fragua said. “First, we tested alternative thresholds to define ‘high metabolic risk,’ and findings show increased risk of dementia to start with the presence of one metabolic syndrome component.
“Second, assessment of metabolic syndrome components in midlife and later life allowed the examination of the role of age at prevalence of metabolic risk for incident dementia at older ages. Third, our findings showed high dementia risk in those free of cardiovascular disease during follow-up, suggesting that the association between high metabolic risk and incident dementia is not fully explained by cardiovascular disease.”
Machado-Fragua added, “For now, a cure for dementia remains elusive, making it important to think of prevention strategies. Our findings support targeting the components of the metabolic syndrome in midlife, even in those who have fewer than three of the metabolic syndrome components.”
Applicability “Confusing”
In an interview, Yehuda Handelsman, MD, questioned the applicability of the study findings in the clinic. “Metabolic syndrome is a clinical manifestation of insulin resistance,” he said. “The more metabolic syndrome criteria a person has, the more insulin resistant that person will be. There is literature that is [suggesting] that insulin resistance is an important cause of dementia.”
The finding of a higher dementia risk before age 70, compared to afterward, makes the applicability “even more confusing,” he said. The results are even more muddled for U.S. physicians, who have moved away from the term metabolic syndrome in favor of cardiometabolic syndrome, said Handelsman, medical director and principal investigator at the Metabolic Institute of America and president of the Diabetes CardioRenal & Metabolism Institute, both in Tarzana, Calif.
Confusion also surrounds one of the components of metabolic syndrome: Waist circumference, per the harmonized definition the study used, and body mass index, which the more traditional definition uses.
Nonetheless, metabolic syndrome can be used as “kind of a risk calculator” for CVD, diabetes, and dementia, he said. One strength of the study, Handelsman said, is its size and scope, following 28 years of data. But a weakness was its observational design. “It doesn’t evaluate any true intervention to modify risk,” he said.
Machado-Fragua and coauthors have no disclosures.
This article originally appeared on MDedge.com, part of the Medscape Professional Network.