An observational study out of the UK has shown an association between higher blood pressure at midlife and increased risk for dementia later in life. After looking at over 8000 subjects, researchers determined that systolic pressure ≥130 mmHg at age 50—but not age 60 or 70—was associated with increased risk of dementia (HR 1.38; 95% confidence interval). Since this was an observational study, it can’t establish whether the higher blood pressure was a causal factor in the increased incidence of dementia. It’s possible they’re both the result of a third, underlying but unidentified factor.

It’s interesting to note that the association between higher blood pressure and increased dementia risk was only found at age 50, and not in older age. The study authors speculated that this could be due to the duration of the hypertension:

“Our analysis suggests that the importance of mid-life hypertension on brain health is due to the duration of exposure. So we see an increased risk for people with raised blood pressure at age 50, but not 60 or 70, because those with hypertension at age 50 are likely to be ‘exposed’ to this risk for longer.” 

The word “hypertension” is problematic here, though. The study found that risk of dementia was increased if systolic pressure was ≥130 mmHg, which is lower than the official threshold for hypertension, at 140 mmHg. This echoes a similar finding from 2013, when it was revealed that individuals with higher average blood glucose well below the threshold for diabetes have higher risk for dementia.

Is there a connection here? If people with blood pressure that’s high, but below the cutoff for hypertension, and blood sugar that’s high, but below the cutoff for diabetes, are at increased risk for developing dementia later in life, what might be behind this?

Chronically elevated insulin could be a factor here. Probably a big factor. Idiopathic or essential hypertension may be driven primarily by chronic hyperinsulinemia, a.k.a. insulin resistance. Insulin resistance is also a major driving factor in Alzheimer’s disease. So it might not be that high blood pressure is causing vascular changes in the brain that influence the development of dementia, although that’s certainly possible. It may be that chronic hyperinsulinemia is behind both hypertension and dementia, and these two seemingly unrelated issues are actually two different manifestations of the same underlying pathology.

Hypertension is included in the official diagnostic criteria for metabolic syndrome, also known as insulin resistance syndrome, which underscores insulin as the driving and unifying pathological factor. So it’s fairly obvious that chronically high insulin is key here, and the same can be said of Alzheimer’s disease, and likely other forms of dementia. We are increasingly seeing certain forms of dementia as falling under the umbrella of “diseases of civilization” driven primarily by diets and lifestyles at odds with what human physiology has evolved to thrive on. (High carb diets and the perhaps overzealous prescription of statin drugs may play roles in the pathology of cognitive decline and impairment.)

Getting back to this study cohort, compared to individuals who did not develop dementia by the end of follow-up, those who did didn’t only have slightly higher blood pressure. They had several other indicators of chronic hyperinsulinemia that might have been missed as being pieces of the puzzle simply because insulin testing is not a routine part of standard bloodwork—although the case can easily be made that it should be! 

Compared to non-demented subjects, the subjects who developed dementia had very slightly higher blood pressure, significantly greater incidence of cardiovascular disease, a-fib and heart failure, more of them currently smoked, more had diabetes, slightly higher BMI, and more reported low levels of physical activity. Cardiovascular disease is largely driven by chronic hyperinsulinemia, physical activity may help promote insulin sensitivity, and chronically elevated insulin is a major driver of overweight and obesity (it directly inhibits lipolysis, making it difficult to lose weight as well), so it stands to reason that high insulin may be the underlying culprit linking together higher blood pressure and increased risk for dementia.       

As we learn more about the myriad unexpected effects of insulin that have nothing to with regulating blood sugar, more is revealed about just how powerfully this hormone influences far more than blood glucose. And it directs healthcare practitioners to guide their patients toward dietary and lifestyle strategies that maintain healthy insulin levels.