Alzheimer’s Disease, the most frequent cause of dementia, may play favorites when it comes to gender.

A new study released Wednesday, March 16, in Neurology has suggested the physical progression of Alzheimer’s may differ between men and women. Studying people with both early Alzheimer's and mild cognitive impairment, the researchers found that even when men and women had the same level of brain deterioration, women generally had better verbal memory. The mismatch only disappeared at higher levels of brain shrinkage.

"One way to interpret the results is that because women have better verbal memory skills than men throughout life, women have a buffer of protection against loss of verbal memory before the effects of Alzheimer's disease kick in,” said lead author Dr. Erin E. Sundermann, of the Albert Einstein College of Medicine, in a statement.

Sundermann and her colleagues turned to data from the Alzheimer’s Disease Neuroimaging Initiative, a long-term study of the condition in existence since 2005. They looked at the MRI scans of 1,308 elderly participants alongside their performance on a variety of tests that measured cognitive ability. Of the sample, 694 had a form of mild cognitive impairment that primarily affected their memory, 235 had full blown Alzheimer’s, and 379 were cognitively healthy.

To determine brain damage, the researchers contrasted the volume of the hippocampal area to total brain volume. Those with a smaller ratio had more deterioration. In the group with mild cognitive impairment and Alzheimer’s, there was a distinct female advantage in verbal memory among those with large to moderate ratios. That advantage vanished among those with small ratios. Contrary to the researchers’ prior speculation, there was also an advantage for women with full Alzheimer’s, though to a lesser degree than in the other two groups. Women also had slightly higher ratios than men on average, reaffirming some but not all prior research on the subject.

The researchers believe their findings may also explain a curious paradox often observed by doctors: Women are more likely to be diagnosed with Alzheimer’s but seemingly less likely to have this form of mild cognitive impairment than men.

“Because verbal memory tests are used to diagnose people with Alzheimer's disease and its precursor, mild cognitive impairment, these tests may fail to detect mild cognitive impairment and Alzheimer's disease in women until they are further along in the disease," explained Sundermann.

Eventually, she and her team speculate, women with worsening brain deterioration experience an accelerated decline that leads them to be diagnosed with Alzheimer’s more often than men. They noted that their current study, which only looked in on patients at one point in time, can’t concretely confirm whether this is the case, however.

The researchers concluded that their findings, if replicated, suggest the need to figure out whether women are diagnosed with mild cognitive impairment at later stages of the disease than men because of this advantage.

“If so, then sex-based norms in clinical memory tests might improve diagnostic accuracy in women,” they wrote.

Alzheimer's has afflicted 5.3 million Americans as of 2015, according to the Alzheimer’s Association.

Source: Sundermann E, Biegon A, Rubin L, et al. Better verbal memory in women than men in MCI despite similar levels of hippocampal atrophy. Neurology. 2016.