In a previous Newsletter I have talked about the dementia study in the Lancet.(Newsletter #175 Is Dementia a Lifestyle Issue?) It showed the fourteen key factors associated with an increased probability of getting dementia. They accounted for 45% of the variation in dementia incidence. In early life they found an association with lower education levels. In mid-life there were ten factors. These included untreated hearing loss, traumatic head injury and hypertension. There were a group of factors more associated with cardiovascular health. These included high cholesterol; diabetes; smoking; physical inactivity, excessive alcohol and obesity. Depression was also a factor. In older age the factors were social isolation, air pollution and untreated sight loss.

In a recent US National Academies workshop one author focused only on one factor. He argued that the early years of education are crucial. The years in which we build our cognitive function reserve. That reserve then declines over the rest of our lives. There is a threshold of decline. If we go past it, then we would be diagnosed with dementia. Some people reach that threshold earlier than others. Many never reach it.

Building Cognitive Reserves

The researchers used large longitudinal studies. They related years of education to the risk of dementia in later life. What was the shape of the curve? Is it a simple straight-line decline? The more years of education the lower your risk of dementia? Or, are there a series of “step functions”. Your risk of dementia drops when you get a degree or a higher degree. It remains flat until that point, drops and then becomes flat again. There is a hybrid model which combines the two. Incidence declines with each year of education. It accelerates when a threshold is reached. It then returns to the same less steep decline.

Education can have huge knock-on effects on the rest of our lives. On our income, on our lifestyles. On the environment in which we live. Was the effect direct or through these other influences.

The results are striking. For many segments of the population there is a simple direct line relationship. The more years of education the lower the incidence of dementia. This is the typical response for women. Some groups such as white males have a hybrid model. They decline in a straight line but there is a single threshold in their curve. There is an acceleration in decline if they graduate from high school. Either side of that point, each year of education yields the same reduction in incidence. On average the incidence declines by 11% for each year.

The team spent a long time looking at the impact of all the other factors that might influence these curves. They included all the benefits that might have come from higher education and could be related to the incidence of dementia. They found no effect across all the different segments of the population. They included early life factors and factors later in life. The results were remarkably robust.

Why is the Incidence of Dementia Declining?

Across the world, study after study are showing that your chance of getting dementia is declining. As the population ages there are more sufferers but the incidence is going down, This data showed the same effect. The looked at the decline over the 18 years from 2000 to 2018. They highlighted that there is not just one incidence. Black Americans aged above 75 started with a much higher chance. Other Black Americans between 65 and 75 had a lower incidence. The white groups were lower still. All older groups had a higher incidence than their younger companions. All were showing a decline in incidence across the period.

They then controlled in their analysis for known dementia incidence influences. They looked at many factors. These included things like smoking, medication and body mass index. Nothing changed the shape of the curve. But, if the included education the curves became flat. Education was explaining the bulk of the differences.

Too Late to Go Back to School

We should all be worried about the education of children. They should all be encouraged to reach their potential. This study provides one more reason. It will prevent dementia in later life. But for most of us it is too late. We can’t go back. Can we do anything to help ourselves?

Another panellist at the National Academies offered some guidelines. They had looked at the original 14 factors for more evidence. They looked particularly for controlled experiments. There were five factors with stronger evidence and which might be modifiable. Things we might be able to do something about. These included physical activity and sleep. Depression and traumatic brain injury. They included hypertension, diabetes and high cholesterol under the banner of “cardiovascular”.

Fixing these would improve general health as well as cognitive health. The first thing they pointed out was that there is no simple solution that fits everybody. Sensitivity to these different factors varies. It varies by race and sex. Any solution has to be customized to the individual. The key issue when trying to change a risk factor it seems is motivation. Results from “one size fits all” intervention trials show some statistically significant improvements but at a very low level. Allowing individuals to customize their program improves the impact dramatically. Letting them pick one or two things to focus on. Tackling many factors at the same time also helps.

We can help our children’s future health by encouraging them to stay in school. We can help ourselves by focusing on a few changes. We need to be motivated and we need to tackle more than one thing at a time. It can do no harm and is good for us.