From the Whitehall II study, data involving 5431 older participants (45-69 at baseline) has revealed a significant effect of midlife sleep changes on later cognitive function. Sleep duration was assessed at one point between 1997 and 1999, and again between 2002 and 2004. A decrease in average night’s sleep from 6, 7, or 8 hours was significantly associated with poorer scores on tests of reasoning, vocabulary, and the MMSE. An increase from 7 or 8 hours (but not from 6 hours) was associated with lower scores on these, as well as on tests of phonemic and semantic fluency. Short-term verbal memory was not significantly affected. The magnitude of these effects was equivalent to a 4–7 year increase in age.

Around 8% of participants showed an increase from 7-8 hours of sleep over the five-year period (7.4% of women; 8.6% of men), while around a quarter of women and 18% of men decreased their sleep amount from 6-8 hours. About 58% of men and 50% of women reported no change in sleep duration during the study period. Some 27% of the participants were women.

The optimal amount of sleep (in terms of highest cognitive performance) was 7 hours for women, closely followed by 6 hours. For men, results were similar at 6, 7 and 8 hours.

Analysis took into account age, sex, education and occupational status. The Whitehall II study is a large, long-running study involving British civil servants. Sleep duration was assessed simply by responses to the question "How many hours of sleep do you have on an average week night?"

A very large Chinese study, involving 28,670 older adults (50-85), of whom some 72% were women, also supports an inverted U-shaped association between sleep duration and cognitive function, with 7-8 hours sleep associated with the highest scores on a delayed word recall test.

I would speculate that this finding of an effect of short-term verbal memory (in contrast to that of the Whitehall study) may reflect a group distinction in terms of education and occupation. The Whitehall study is the more homogenous (mostly white-collar), with participants probably averaging greater cognitive reserve than the community-based Chinese study. The findings suggest that memory is slower to be affected, rather than not affected.

Comparison of young adults (mean age 24.5) and older adults (mean age 69.1) in a visual memory test involving multitasking has pinpointed the greater problems older adults have with multitasking. The study involved participants viewing a natural scene and maintaining it in mind for 14.4 seconds. In the middle of the maintenance period, an image of a face popped up and participants were asked to determine its sex and age. They were then asked to recall the original scene.

As expected, older people had more difficulty with this. Brain scans revealed that, for both groups, the interruption caused their brains to disengage from the network maintaining the memory and reallocate resources to processing the face. But the younger adults had no trouble disengaging from that task as soon as it was completed and re-establishing connection with the memory maintenance network, while the older adults failed both to disengage from the interruption and to reestablish the network associated with the disrupted memory.

This finding adds to the evidence that an important (perhaps the most important) reason for cognitive decline in older adults is a growing inability to inhibit processing, and extends the processes to which that applies.

A two-year study involving 53 older adults (60+) has found that those with a mother who had Alzheimer's disease had significantly more brain atrophy than those with a father or no parent with Alzheimer's disease. More specifically, they had twice as much gray matter shrinkage, and about one and a half times more whole brain shrinkage per year.

This atrophy was particularly concentrated in the precuneus and parahippocampal gyrus. Those with the APOE4 gene also had more atrophy in the frontal cortex than those who didn’t carry the ‘Alzheimer’s gene’.

This adds to evidence indicating that maternal history is a far greater risk factor for Alzheimer’s than paternal history. Eleven participants reported having a mother with Alzheimer's disease, 10 had a father with Alzheimer's disease and 32 had no family history of the disease. It has been estimated that people who have first-degree relatives with Alzheimer's disease are four to 10 times more likely to develop the disease.

Shrinking of the frontal lobe has been associated with age-related cognitive decline for some time. But other brain regions support the work of the frontal lobe. One in particular is the cerebellum. A study involving 228 participants in the Aberdeen Longitudinal Study of Cognitive Ageing (mean age 68.7) has revealed that there is a significant relationship between grey matter volume in the cerebellum and general intelligence in men, but not women.

Additionally, a number of other brain regions showed an association between gray matter and intelligence, in particular Brodmann Area 47, the anterior cingulate, and the superior temporal gyrus. Atrophy in the anterior cingulate has been implicated as an early marker of Alzheimer’s, as has the superior temporal gyrus.

The gender difference was not completely unexpected — previous research has indicated that the cerebellum shrinks proportionally more with age in men than women. More surprising was the fact that there was no significant association between white memory volume and general intelligence. This contrasts with the finding of a study involving older adults aged 79-80. It is speculated that this association may not develop until greater brain atrophy has occurred.

It is also interesting that the study found no significant relationship between frontal lobe volume and general intelligence — although the effect of cerebellar volume is assumed to occur via its role in supporting the frontal lobe.

The cerebellum is thought to play a vital role in three relevant areas: speed of information processing; variability of information processing; development of automaticity through practice.

The new label of ‘metabolic syndrome’ applies to those having three or more of the following risk factors: high blood pressure, excess belly fat, higher than normal triglycerides, high blood sugar and low high-density lipoprotein (HDL) cholesterol (the "good" cholesterol). Metabolic syndrome has been linked to increased risk of heart attack.

A new French study, involving over 7,000 older adults (65+) has found that those with metabolic syndrome were 20% more likely to show cognitive decline on a memory test (MMSE) over a two or four year interval. They were also 13% more likely to show cognitive decline on a visual working memory test. Specifically, higher triglycerides and low HDL cholesterol were linked to poorer memory scores; diabetes (but not higher fasting blood sugar) was linked to poorer visual working memory and word fluency scores.

The findings point to the importance of managing the symptoms of metabolic syndrome.

High cholesterol and blood pressure in middle age tied to early memory problems

Another study, involving some 4800 middle-aged adults (average age 55), has found that those with higher cardiovascular risk were more likely to have lower cognitive function and a faster rate of cognitive decline over a 10-year period. A 10% higher cardiovascular risk was associated not only with increased rate of overall mental decline, but also poorer cognitive test scores in all areas except reasoning for men and fluency for women.

The cardiovascular risk score is based on age, sex, HDL cholesterol, total cholesterol, systolic blood pressure and whether participants smoked or had diabetes.

Memory problems may be sign of stroke risk

A very large study (part of the REGARDS study) tested people age 45 and older (average age 67) who had never had a stroke. Some 14,842 people took a verbal fluency test, and 17,851 people took a word recall memory test. In the next 4.5 years, 123 participants who had taken the verbal fluency test and 129 participants who had taken the memory test experienced a stroke.

Those who had scored in the bottom 20% for verbal fluency were 3.6 times more likely to develop a stroke than those who scored in the top 20%. For the memory test, those who scored in the bottom 20% were 3.5 times more likely to have a stroke than those in the top quintile.

The effect was greatest at the younger ages. At age 50, those who scored in the bottom quintile of the memory test were 9.4 times more likely to later have a stroke than those in the top quintile.

Together, these studies, which are consistent with many previous studies, confirm that cardiovascular problems and diabetes add to the risk of greater cognitive decline (and possible dementia) in old age. And point to the importance of treating these problems as soon as they appear.