For patients with Alzheimer’s disease, it helps to have a big head.

That’s the conclusion of a new study that examined the head circumferences of 270 participants in the Multi-Institutional Research in Alzheimer’s Genetic Epidemiology study (or MIRAGE for short). Apparently, the extra cranial capacity affords patients some cognitive reserve, resulting in better brain function at any given level of cerebral atrophy.

Researchers had previously noted an inverse relationship between cognitive performance and head circumference. But whether one’s “maximum attained brain size” affected the relationship between brain pathology and Alzheimer’s symptoms remained unknown, according to the new report.

To find out, German researchers working on the MIRAGE study gathered all sorts of data on 270 patients, whose average age was 75. They measured their heads (as a proxy for brain volume). They gave them MRI scans to ascertain their degree of cerebral atrophy (as a proxy for the damage wrought by Alzheimer’s). They took blood to see which variant of the APOE gene was in their DNA (having one or two copies of the e4 version of APOE is thought to increase one’s risk of Alzheimer’s). They looked up the results of each patient’s most recent mini-mental state examination (MMSE) to measure cognitive function. They also took into account each patient’s age and ethnicity, how long they’d had Alzheimer’s and whether they had diabetes, hypertension or major depression.

Not surprisingly, the researchers found that patients with higher MMSE scores had less severe brain atrophy and had been diagnosed more recently. But head circumference seemed to have no bearing on it.

Then they adjusted their equations to look specifically for a relationship between brain atrophy and head circumference. At all levels of atrophy, patients with bigger heads were able to get higher MMSE scores than their smaller-headed counterparts.

“Our results support the concept of BR [brain reserve] and underline the importance of optimal neurological development in early life,” the researchers wrote.

How early? If you can read this, it’s probably too late for you.

Studies show that brains reach 93% of their maximum size when they are only 6 years old. Bigger brains have more neurons, as well as more connections between them. Genetics plays a role, but so do external factors such as nutrition, central nervous system infections and brain injury early in life.

The upshot is that Alzheimer’s prevention efforts should be geared toward the preschool set, the German researchers suggested. Here’s how they put it:

“The improvement of perinatal and early life conditions could significantly increase BR in the population, which in turn may have an impact on the risk of developing AD [Alzheimer’s disease] or the severity of symptoms in AD.”

The results will be published in Tuesday’s edition of the journal Neurology.