More evidence that vascular disease plays a crucial role in age-related cognitive impairment and Alzheimer’s comes from data from participants in the Alzheimer's Disease Neuroimaging Initiative.

The study involved more than 800 older adults (55-90), including around 200 cognitively normal individuals, around 400 people with mild cognitive impairment, and 200 people with Alzheimer's disease. The first two groups were followed for 3 years, and the Alzheimer’s patients for two. The study found that the extent of white matter hyperintensities (areas of damaged brain tissue typically caused by cardiovascular disease) was an important predictor of cognitive decline.

Participants whose white matter hyperintensities were significantly above average at the beginning of the study lost more points each year in cognitive testing than those whose white matter hyperintensities were average at baseline. Those with mild cognitive impairment or Alzheimer's disease at baseline had additional declines on their cognitive testing each year, meaning that the presence of white matter hyperintensities and MCI or Alzheimer's disease together added up to even faster and steeper cognitive decline.

The crucial point is that this was happening in the absence of major cardiovascular events such as heart attacks, indicating that it’s not enough to just reduce your cardiovascular risk factors to a moderate level — every little bit of vascular damage counts.

There have been mixed findings about the benefits of DHA (an omega-3 fatty acid), but in a study involving 485 older adults (55+) with age-related cognitive impairment, those randomly assigned to take DHA for six months improved the score on a visuospatial learning and episodic memory test. Higher levels of DHA in the blood correlated with better scores on the paired associate learning task. DHA supplementation was also associated with better verbal recognition, but not better working memory or executive function.

Other research has found no benefit from DHA to those already with Alzheimer’s, although those with Alzheimer’s tend to have lower levels of DHA in the blood. These findings reinforce the idea that the benefit of many proactive lifestyle strategies, such as diet and exercise, may depend mainly on their use before systems deteriorate.

The daily dose of algal DHA was 900 mg. The study took place at 19 clinical sites in the U.S., and those involved had an MMSE score greater than 26.

Do retired people tend to perform more poorly on cognitive tests than working people because you’re more likely to retire if your mental skills are starting to decline, or because retirement dulls the brain?

For nearly 20 years the United States has surveyed more than 22,000 Americans over age 50 every two years, and administered memory tests. A similar survey has also been taking place in Europe. A comparison of the 2004 data for the U.S., England, and eleven European countries (Austria, Belgium, Denmark, France, Germany, Greece, Italy, The Netherlands, Spain, Sweden, and Switzerland) has now revealed differences in the level of cognitive performance among older adults between the countries (the 60-64 year age group was used as it represents the greatest retirement-age difference between nations).

These differences show some correlation with differences in the age of retirement. Moreover, the differences also correlate to differences in government policy in terms of pensions — supporting the view that it is retirement that is causing the mental decline, not the decline that brings about early retirement.

Memory was tested through a simple word recall task — recalling a list of 10 nouns immediately and 10 minutes later. People in the United States did best, with an average score of 11 out of a possible 20. Those in England were very close behind, and Denmark and Sweden were both around 10. Switzerland, Germany and the Netherlands, and Austria were all clustered between 9 and 9 ½; Belgium and Greece a little lower. France averaged 8; Italy 7; Spain (the lowest) just over 6.

Now when the average cognitive score is mapped against the percentage of retired for 60-64 year olds, the points for each country (with one exception) cluster around a line with a slope of -5, indicating that there is a systematic relationship between these two variables, and that on average being retired is associated with a lower memory score of about 5 points on a 20-point scale. This is a very large effect.

But the correlation is not (unsurprisingly) exact. Although the top scorers, U.S., England and Denmark, are among those nations who have lower retirement rates at this age, Switzerland has the same levels as the U.S., and Sweden has the fewest retired of all (around 40% compared to around 47% for the U.S. and Switzerland). Most interesting of all, why does Spain, which has around 74% retired, show such a low cognitive score, when five other countries have even higher rates of retirement (Austria has over 90% retired)?

There are of course many other differences between the countries. One obvious one to look at would be the degree to which older people who are not working for pay are involved in voluntary work. There’s also the question of the extent to which different countries might have different occupation profiles, assuming that some occupations are more mentally stimulating than others, and the degree to which retired people are engaged in other activities, such as hobbies and clubs.

The paper also raises an important point, namely, that retirement may be preceded by years of ‘winding-down’, during which workers become progressively more reluctant to keep up with changes in their field, and employers become increasingly reluctant to invest in their training.

A Chinese study involving 153 older men (55+; average age 72), of whom 47 had mild cognitive impairment, has found that 10 of those in the MCI group developed probable Alzheimer's disease within a year. These men also had low testosterone, high blood pressure, and elevated levels of the ApoE4 protein.

The findings support earlier indications that low testosterone is associated with increased risk of Alzheimer's in men, but it’s interesting to note the combination with high blood pressure and having the ApoE4 gene. I look forward to a larger study.

Data from 21,123 people, surveyed between 1978 and 1985 when in their 50s and tracked for dementia from 1994 to 2008, has revealed that those who smoked more than two packs per day in middle age had more than twice the risk of developing dementia, both Alzheimer's and vascular dementia, compared to non-smokers.

A quarter of the participants (25.4%) were diagnosed with dementia during the 23 years follow-up, of whom a little over 20% were diagnosed with Alzheimer's disease and nearly 8% with vascular dementia.

Former smokers, or those who smoked less than half a pack per day, did not appear to be at increased risk. Associations between smoking and dementia did not vary by race or sex.

Smoking is a well-established risk factor for stroke, and is also known to contribute to oxidative stress and inflammation.