Men May Be More Susceptible to Mild Cognitive Impairment than Women

MCI is often considered a precursor to dementia and Alzheimer's disease, although that view remains controversial.

Men may be more vulnerable than women to developing mild cognitive impairment (MCI) as they age, according to new research from the Mayo Clinic.

MCI — defined as a decline in thinking and memory skills that's more pronounced than that typically associated with aging — is often considered a precursor to dementia and Alzheimer's disease, although that view remains controversial.

The finding that more older men than older women develop MCI was "very surprising" because women are generally believed to have higher rates of dementia, said Dr. Rosebud Roberts, an epidemiologist at Mayo and the lead author of the study, in a phone interview Thursday.

The finding suggests, she added, that the progression from MCI to dementia may be different for each gender.

Confirmation of previous finding:

If this study's results seem like déjà vu to you, it's because Mayo researchers reported in 2010 that the prevalence of MCI was higher in men than in women. But that finding reflected only a snapshot of what was happening in a population at a single moment. The current study followed healthy people for several years and observed how many developed MCI.

"This is a more robust type of study, a more definitive study," said Roberts.
For the study, Roberts and her colleagues followed 1,450 residents of Minnesota's Olmstead County. The participants, aged 70 to 89 at the study's onset, were given neurological tests and evaluations every 15 months for an average of about three years. All were free of signs of cognitive decline at the start of the study.

By the study's end, 296 had developed MCI — and the rate of those cases was significantly higher among men (72 per 1,000 people) than among women (57 per 1,000).
The study found that individuals who were unmarried or who had not attended college were also more likely to develop MCI, but the more-men-then-women finding is the one that has researchers perplexed.

As Dr. Kenneth Rockwood, a professor of geriatric medicine at Dalhouse University in Nova Scotia, notes in an editorial accompanying the Mayo study, "it is unclear how to square more men in the at-risk state not translating into more men with dementia."

After all, studies have generally not found men to have the higher risk of dementia. In Olmstead County, said Roberts, the dementia risk is the same for men and women, but other research, particularly from Europe, suggests the risk is higher in women.

"We are now trying to find out what happens when men and women develop MCI," Roberts said. "One of our hypotheses is that women could possibly progress faster to dementia once they develop MCI, whereas men might stay in the MCI phase for longer. We are currently studying this."
"If women progress faster," she added, "then even if men are staying at the same rate, we might find that there is no sex difference in dementia or we may find women may have a higher incidence of dementia. That's the next story that remains to be told."

A valid predictor?

Of course, the Mayo study is built on the assumption that MCI is a valid predictor of dementia. But not everybody accepts that idea, as I reported when the 2010 Mayo study was published.
"[MCI] is an example of labeling what is a continuum of brain aging that we all go through," Dr. Peter J. Whitehouse, a neurologist and founder of the Memory and Cognition Center at Case Western Reserve University and one of MCI's leading skeptics, said.

No one can say with any certainty, he added back then, which people with MCI will go on to develop dementia and which ones won't.

As Roberts herself acknowledged, only about 10 percent of people with MCI go on to develop full-blown dementia. That compares to about 1 percent of people without MCI, she said.
That means, of course, that 90 percent of people with MCI will never develop dementia.
There's also the problem of reversion. In the current Mayo study, for example, one-third of the people diagnosed with MCI (or 12 percent per year) were later diagnosed at least once during the study as not having the condition.

In his editorial, Rockwood speculates that the positive reversal of symptoms seen in the Mayo study may indicate that "cognitive aging represents not just relentless decline — the brain as innocent bystander — but the outcomes of a struggle between insults and repair mechanisms."
Or could the reversion simply indicate, as Whitehouse claims, that MCI is so ill-defined that it is meaningless as a quantifier of dementia risk?

A need for prevention

One thing that everybody involved in dementia research can agree on is the need for more prevention, which includes reducing the incidence of the usual suspects: obesity, type 2 diabetes and high blood pressure.

"If we could reduce the burden of these diseases in the population, we hope we can reduce the risk of MCI and dementia," said Roberts.

The Mayo Clinic study appears in the Jan. 25 issue of the journal Neurology.

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