Doubling down on trace minerals may impair cognitive function, experts warn

31 Jan 2023 --- A new study reveals a significant link between a higher intake of the trace minerals copper and iron, and cognitive decline. Yet, the researchers hold that further studies must be conducted to confirm their initial findings.

The study evaluated dietary consumption of four trace minerals – iron, copper, zinc and manganese. Though manganese and zinc show no correlation – either negative or positive on cognitive ability – elevated amounts of dietary iron and copper are associated with “worse cognitive function.”

The cross-sectional study includes 6,863 participants – 2,794 men and 4,069 women with an average age of 66.7 (plus or minus 10.5 years). It further utilized data from the Health and Retirement Study (HRS) and the Health Care and Nutrition Study (HCNS) – both of which were conducted in the US in 2013 and 2014, respectively.

Unhealthy aging?
According to the study, published in Nutrients, there are several biological pathways by which trace minerals could be associated with brain health. Zinc is a key component of many brain enzymes and may play a role in combating neurodegenerative diseases like Alzheimer’s. However, copper was also shown to have a similar correlation in animal studies.

Cognition was measured via a modified telephone interview and and compared to dietary biomarkers.Additionally, magnesium has been shown to improve mood, facilitate restful sleep and even reduce blood pressure. Iron deficiency can lead to anemia, which can adversely affect quality of life, and iron has also been shown to reduce neuronal inflammation.

 However, the researchers state that this is one of the first and largest studies of its kind – focusing solely on humans instead of animal-based models. Moreover, it is one of the only studies to focus on previous epidemiologic research showing higher levels of iron and copper and lower levels of zinc and magnesium and the association with cognitive decline.

“In the context of global aging, cognitive impairment and dementia – regarded as the major causes of disability and mortality in older adults – place a great burden on healthcare systems and resources,” the researchers state. “The lack of effective treatments for dementia makes it important to identify its risk factors for primary prevention.”

Testing the brain
Cognition was measured via an adapted version of the Telephone Interview for Cognitive Status (TICS). The TICS utilized an immediate and a delayed 10-noun free recall test (two iterations for a 20-point total), counting backward from 20 (two iterations for a four-point total) and serial seven subtractions – where the interviewees consecutively subtracted seven from 100 (five iterations for five-points total). 

Cognitive impairment was accessed if the participant was unable to score more than 12 points.

The result of the TICS was then compared to the participants’ dietary intake levels as assessed by the Harvard Food Frequency Questionnaire (FFQ) and validated against multiple 24-hour recall interviews and relevant biochemical markers.

Moderation may be keyThe study found that exceeding dietary recommendations of iron and copper could affect cognition later in life.
The results corroborate former findings showing that higher dietary iron and copper intake levels are correlated with decreased cognitive functions. However, this correlation only occurs in subjects whose dietary intake greatly exceeds daily recommended allowances (DRAs). 

For iron, the participants with decreased cognitive function took an average of greater than or equal to 17.7 mg per day, more than twice the DRA of 8 mg per day. For copper, it was the same, with decreased cognitive function participants taking more than or equal to 1.8 mg per day as opposed to the recommended 0.9 mg.

However, the researchers also reported a “non-significant association for zinc and manganese intake,” meaning that the two minerals had no effect on cognition whether the participants were deficient or took them at higher than recommended levels.

“There are several limitations that need to be taken into account when interpreting our results,” the researchers explain. “First, as a cross-sectional study, the observed associations might not necessarily be causal because reverse causality might exist. The long-term associations of these dietary mineral intake levels with cognitive function are yet to be revealed.”

“Second, dietary intake levels of the minerals of interest were measured by the single FFQ, and measurement errors cannot be avoided. Furthermore, although we made the most possible adjustments for potential confounding factors, residual confounders are inevitable in the observational setting. Specifically, as the nutrients are highly correlated in food groups, we could not rule out the potential confounding influence of other nutrients.”

The study further concludes that more research must be conducted to understand the biological mechanisms that may be affecting cognitive functioning, rule out reverse causality and help establish preventive practices in the area of cognitive decline.

Edited by William Bradford Nichols