Comparison of the brains of 22 smokers and 21 people who have never smoked in their lives has revealed that the left medial orbitofrontal cortex of the smokers was on average smaller than that of the non-smokers. Moreover, this reduction was greater the more cigarettes were smoked daily, and as a function of how long they had smoked. The region is involved in reward, impulse control, and decision-making, suggesting that fewer neurons there may mean you have to work harder for reward, and that your ability to curb your impulses and make decisions is impaired.

While it may be that smoking is affecting this damage, it may also be that those with a smaller orbitofrontal cortex are more likely to smoke (perhaps it is most likely that both are true!). Further research will need to distinguish these two possibilities.

Inflammation in the brain appears to be a key contributor to age-related memory problems, and it may be that this has to do with the dysregulation of microglia that, previous research has shown, occurs with age. As these specialized support cells in the brain do normally when there’s an infection, with age microglia start to produce excessive cytokines, some of which result in the typical behaviors that accompany illness (sleepiness, appetite loss, cognitive deficits and depression).

Now new cell and mouse studies suggests that the flavenoid luteolin, known to have anti-inflammatory properties, apparently has these benefits because it acts directly on the microglial cells to reduce their production of inflammatory cytokines. It was found that although microglia exposed to a bacterial toxin produced inflammatory cytokines that killed neurons, if the microglia were first exposed to luteolin, the neurons lived. Exposing the neuron to luteolin had no effect.

Old mice fed a luteolin-supplemented diet for four weeks did better on a working memory test than old mice on an ordinary diet, and restored levels of inflammatory cytokines in their brains to that of younger mice.

Luteolin is found in many plants, including carrots, peppers, celery, olive oil, peppermint, rosemary and chamomile.

Manganese exposure in the workplace is known to have neurotoxic effects, but manganese occurs naturally in soil and sometimes in groundwater. One region where the groundwater contains naturally high levels of manganese is Quebec. A study involving 362 Quebec children, aged 6-13, has measured both the concentrations of metals (manganese, iron, copper, lead, zinc, arsenic, magnesium and calcium) in their tap water, and their cognitive abilities.

Although manganese concentrations were well below current guidelines, the average IQ of those whose tap water was in the upper 20% was 6.2 points below children whose water contained little or no manganese. The association was more marked for Performance IQ than Verbal IQ (Performance IQ reflects perceptual organization and processing speed). The analysis took into account factors such as family income, maternal intelligence, maternal education, and the presence of other metals in the water. No association was found between manganese in their food and IQ.

A number of studies have found evidence that fruits and vegetables help fight age-related cognitive decline, and this has been thought to be due to their antioxidant and anti-inflammatory effects. A new study shows there may be an additional reason why polyphenols benefit the aging brain. One reason why the brain works less effectively as it gets older is that the cells (microglia) that remove and recycle biochemical debris not only fail to do their housekeeping work, but they actually begin to damage healthy cells. Polyphenols restore normal housekeeping, by inhibiting the action of a protein that shuts down the housekeeping (autophagy) process.

While many fruits and vegetables are good sources of polyphenols, berries and walnuts, and fruit and vegetables with deep red, orange, or blue colors, are particularly good.

A very large study of older women has found that although there was a small downward trend in cognitive function (as measured by the MMSE) with increasing obesity, this trend was almost entirely driven by those with a waist-hip ratio below 0.78 — that is, for women who carry excess weight around their hips, known as pear shapes (as opposed to carrying it around the waist, called apple shapes). The study of 8,745 post-menopausal women (aged 65-79) found a drop of around 2 points on the 100-point MMSE for those with a BMI over 40 compared to those who were of normal weight, after controlling for such variables as education, diabetes, heart disease and hypertension, all of which were also significantly associated with BMI and MMSE score. Because 86% of the participants were white, and women belonging to other ethnic groups were not equally distributed between BMI categories, only data from white women were used. Some 70% of the participants were overweight (36%) or obese (34%).

Fat around the middle is thought to make more estrogen, which protects cognitive function. However, although depositing fat around the waist may be better for the brain, it is said to increase the risk of cancer, diabetes and heart disease.