While previous research has linked higher dietary levels of carotenoids, lutein, and zeaxanthin to better cognitive function, the latest study is the first to demonstrate deficits of such compounds in Alzheimer’s, they claim.
The findings, which were published in the Journal of Alzheimer’s Disease, aimed to test the hypothesis that micronutrients are significantly lower in brains with Alzheimer's disease than in healthy elderly brains.
“This study, for the first time, demonstrates deficits in important dietary antioxidants in Alzheimer’s brains,” said C Kathleen Dorey, professor in the Department of Basic Science Education at the Virginia Tech Carilion School of Medicine.
“These results are consistent with large population studies that found risk for Alzheimer’s disease was significantly lower in those who ate diets rich in carotenoids, or had high levels of lutein and zeaxanthin in their blood, or accumulated in their retina as macular pigment.
“Not only that, but we believe eating carotenoid-rich diets will help keep brains in top condition at all ages.”
Highest antioxidant intakes linked to 50% lower risk of Alzheimer’s disease
The Rush University Memory and Ageing Project followed the diet and cognitive performance of more than 1,000 participants living in Chicago for more than a decade.
It found that following the MIND diet – which emphasises consuming higher quantities of antioxidant-rich foods such as fruits, nuts, vegetables, and fish – was associated with higher cognitive performance before death, a reduced risk of Alzheimer’s diagnosis, and less Alzheimer’s disease-related brain pathology.
Participants with the highest intake of total carotenoids – powerful antioxidants commonly found in colourful plants – or lutein (abundant in kale and spinach) and zeaxanthin (highest in corn and orange peppers) over a decade had a 50% lower risk for Alzheimer’s disease.
Meanwhile, brains with Alzheimer’s neuropathology had significantly lower levels of lutein, zeaxanthin, lycopene, and tocopherols – a group of fat-soluble phenolic compounds that comprise the major forms of vitamin E.
Concentrations of lycopene, zeaxanthin, and retinol were half those found in age-matched brains with no Alzheimer’s pathology.
Alzheimer’s disease linked to lower levels of lutein and beta-carotene
Alzheimer’s disease, a progressive neurodegenerative disease and the most common cause of dementia among older people, is estimated to affect as many as 55 million people worldwide – a figure that is expected to increase as the population ages.
Oxidative stress contributes to disease progression. As normal brain functions and responses to misfolded proteins constantly generate reactive oxidising molecules, the brain is vulnerable to cumulative oxidative damage. However, this can be prevented by consuming antioxidants from a healthy diet.
A lower risk of dementia has also been identified in those with highest levels of lutein and zeaxanthin in their diet or accumulated in their macular pigment, while lower levels of multiple carotenoids have been found in the serum and plasma of patients with the condition.
Higher levels of carotenoids and tocopherols have been associated with better cognitive function and lower risk for Alzheimer's disease.
Diagnosing and limiting future Alzheimer’s disease
This evidence of selective carotenoid and tocopherol deficiencies in Alzheimer’s brains adds to the research showing that higher dietary carotenoid intake may slow cognitive decline before – and possibly even after – diagnosis with the disease.
Research also shows that the retina selectively accumulates lutein and zeaxanthin from the diet, forming visible yellow macular pigment that enhances vision and protects photoreceptors. By noninvasively measuring patients’ macular pigment optical density, researchers can estimate the concentration of lutein and zeaxanthin in the brain.
“Recent advances in new therapies for Alzheimer’s disease show exciting promise as an effective way to slow disease progression,” Dorey said. “I’d be thrilled if our data motivated people to keep their brains in optimum condition with a colourful diet with abundant carotenoids and regular exercise. Available studies suggest this may also reduce risk for dementia.”
