CALCIUM and vitamin D in dairy products may be contributing to brain damage and dementia in older men and women, new research suggests.
Scientists believe too much calcium can narrow blood vessels in the brain, leading to neural damage. The effect may be compounded by vitamin D, which regulates calcium retention and activity.
Researchers made the discovery after scanning the brains of 79 men and 153 women aged between 60 and 86. All had at least a number of brain lesions - areas of tissue damage.
They varied in size and included tiny flaws often seen even in healthy older people. But participants consuming the most calcium and vitamin D were significantly more likely to have a higher total volume of brain lesions. Age, high blood pressure and other medical and mental conditions, including depression, made no difference to the results.
In earlier studies, the same United States team found individuals who consumed high amounts of fatty dairy products had larger numbers of brain lesions.
However, fat intake in general was not a significant factor. The researchers wanted to find out if a factor other than fat caused the harmful effects of a high dairy diet.
The findings, presented at a conference in Washington entitled Experimental Biology, point to calcium, which is abundant in dairy foods. Its regulator, vitamin D, is also found in many dairy products as well as vitamin-fortified foods such as margarine, cereals and bread.
The study leader, Dr Martha Payne, of Duke University in Durham, North Carolina, said: "We do not know if high calcium and vitamin D intake are involved with the causation of brain lesions, but the study provides support to the growing number of researchers who are concerned about the effects of too much calcium, particularly among older adults, given the current emphasis on promoting high intakes of calcium and vitamin D."
Her team is continuing to investigate possible ways in which high levels of calcium and vitamin D might damage the brain.
The leading theory is that when too much calcium is absorbed into blood vessel walls, it produces bone-like deposits. This calcification may narrow the blood vessels and make them less flexible, reducing the blood flow through them.
In the brain, neurons could be deprived of blood and die, causing the lesions that increase the risk of cognitive impairment, dementia, depression and strokes.
A previous study published last year by Columbia University Medical Centre suggested eating a "Mediterranean-style" diet significantly reduced the risk of developing Alzheimer's disease.
Such a diet - rich in fruit, vegetables and cereals with some fish and alcohol and very little dairy and meat - has been long associated with a healthy lifestyle.
The food intake of participants was given a Mediterranean diet score of between zero and nine.
The researchers found that, for each additional point on the Mediterranean diet scale, the risk of Alzheimer's dropped by almost 10 per cent.