October 25, 2019
Participants with the highest concentrations of serum elaidic acid, a major trans-fatty acid formed in the partial hydrogenation of vegetable oils, had a 53% increased risk of dementia. This group also had a 43% higher likelihood for developing AD compared with those with the lowest levels.
"We found that higher serum elaidic acid levels were associated with greater risk of developing all-cause dementia and Alzheimer's disease, after adjustment for traditional risk factors as well as dietary saturated and polyunsaturated fatty acids intake," principal investigator Toshiharu Ninomiya, MD, PhD, told Medscape Medical News.
"In addition, the self-reported intake of breads, margarine and confectioneries were correlated with serum elaidic acid levels, although the magnitude of the correlation was not strong," added Ninomiya, a professor in the Departments of Epidemiology and Public Health and the Center for Cohort Studies, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
The study was published online October 23 in Neurology.
Given these health concerns, the FDA banned artificial trans fats from grocery store and restaurant foods in June 2018. The agency permits foods with less than 0.5 grams of trans fats to be labeled as containing zero grams of trans fats, so some foods still contain partially hydrogenated oils.
"These results give us even more reason to avoid trans fats," Ninomiya said in a news release. "In the United States, the small amounts still allowed in foods can really add up if people eat multiple servings of these foods, and trans fats are still allowed in many other countries."
The World Health Organization also is taking action with an initiative to eliminate industrial trans fat from the global food supply by 2023.
However, less is known about any potential association between trans fat and dementia. The few studies in the literature have yielded inconsistent results, the researchers note.
In search of a more definitive answer, the investigators assessed data from 1628 participants in the ongoing, prospective Hisayama Study. The 925 women and 703 men completed questionnaires and provided blood samples in 2002 to 2003. All were 60 years or older at baseline.
The researchers also classified serum levels of elaidic acid into quartiles, and then followed participants prospectively for a median of 10.3 years.
Participants completed the Diet History Questionnaire, reporting intake of 150 food items in 23 categories. The researchers focused on seven of these food groups known to contain trans fats, including cereals, confectioneries, animal and plant fat, sugar and sweeteners, seasonings, meat, and dairy products.
Over more than a decade of follow-up, 377 participants developed all-cause dementia, including 247 who developed AD and 102 who developed vascular dementia.
Using the lowest quartile of serum elaidic age concentration group as a reference, the likelihood for developing all-cause dementia significantly increased with higher serum trans-fat groups. For example, the second quartile cohort had a hazard ratio (HR) of 1.24 (95% confidence interval [CI], 0.92 - 1.68; P = .16).
Findings for the third quartile (HR, 1.63; 95% CI, 1.21 - 2.18; P = .001) and the fourth and highest serum quartile (HR, 1.53; 95% CI, 1.14 - 2.04; P = .004) also were noteworthy.
"Although significant linear trends were observed, the risk of developing dementia and AD appeared to increase at the level of the third quartile," the researchers note.
Again, using the lowest serum trans-fat cohort as reference, the risk for developing AD increased with increasing concentrations of elaidic acid. The hazard ratios were 1.22, 1.79, and 1.43 for the second, third, and fourth quartiles, respectively.
Pastries, Margarine, Candy
The association between serum elaidic acid and risk of all-cause dementia and AD remained in a multivariable model that adjusted for age, sex, education, hypertension, diabetes, total cholesterol, BMI, history of stroke, and other traditional risk factors. This model also adjusted for total energy intake, as well as intake of saturated and polyunsaturated fatty acids.
Investigators found no significant association between higher elaidic acid levels and risk of vascular dementia.
"Since serum elaidic acid levels are likely to reflect industrially produced trans-fat intake, our findings raise the possibility that avoiding the intake of foods high in trans fat may reduce the risk of future onset of dementia," Ninomiya said.
Sweet pastries were the strongest predictor of higher serum elaidic levels, followed by margarine and sugar confections such as candy, caramels, and chewing gum. Croissants, nondairy creamers, ice cream, and rice crackers were also associated with higher trans-fat levels in the study.
"Public health policy to augment food industry efforts to reduce trans-fatty acids in the food supply and to educate the public about healthy food choices may additively contribute to the primary prevention of dementia," the researchers note.
The mechanisms underlying the link between serum elaidic acid levels and dementia are still unknown, Ninomiya said. More research is necessary to confirm these findings, she added.
A potential limitation is that all participants were from the same town in Japan and levels of trans fats in the diet vary by country, region, and time period. Therefore, the results may not apply to other populations, the researchers note.
A "Good News Story"
The study is "definitely interesting. There is a growing body of evidence between diet and risk of dementia. And it's probably about people not getting enough green leafy vegetables, nutrients, or vitamin B, for example," Keith Fargo, PhD, director of scientific programs and outreach at the Alzheimer's Association in Chicago, told Medscape Medical News.
"The risk could also be related to environmental toxins, where people are exposed via food or environmental pollution," he added.
Caution is warranted but the study is about associations and not causation, Fargo noted. "The authors did a good job of controlling for other factors, but it is impossible to control for everything," he said.
"I would consider this a good news story. In the US, we have largely banned trans fats, and this could be good news for future dementia levels," Fargo said. "This is another piece of evidence to support the FDA's actions."
The Japanese Ministry of Education, Culture, Sports, Science, and Technology; the Japanese Ministry of Health, Labor, and Welfare; and the Japan Agency for Medical Research and Development supported the research. Ninomiya and Fargo have disclosed no relevant financial relationships.