Cardiovascular risk factors in middle age such as diabetes and hypertension are linked to greater cognitive decline. David Knopman and his associates from the Mayo Clinic in Rochester propose that their study adds more incentive to treat these chronic health problems aggressively and earlier.

How was the study conducted?

The authors followed almost 11,000 people between 47 and 70 years of age for an average of six years.

At the outset of the study the subjects were given a battery of cognitive ability tests as well as blood pressure measurements, serum lipid and sugar studies and high resolution ultrasound to assess the thickness of their carotid arteries (a measurement of atherosclerosis).

The testers also sought information by questionnaire about other potentially confounding factors such as smoking, education and medical history.

What did the results reveal?

Not unexpectedly, the greatest cognitive decline was in the older subjects. However, having diabetes and/or hypertension emerged as independent risk factors for further cognitive decline as seen by lower scores on two of the cognitive ability tests over time.

• Diabetes was a risk factor for subjects of all ages, while hypertension increased the risk only for older subjects (over 58 years of age).
  
  
• On the other hand, smoking, having a thicker carotid artery intima media and using anti-inflammatory drugs had no discernable effect on cognitive decline.

The authors suggested that the possible mechanism of cognitive decline in hypertension and diabetes might be the demyelination or micro-infarction of the cerebral white matter. 

What did the study add?

Other studies have also examined the link between hypertension and diabetes and dementia and suggest that both diseases may be independent risk factors for cognitive impairment or dementia.

The authors pointed out that as the degree of cognitive decline was only relatively minor, it may not have made much of a difference to the subjects' lives on a daily basis.

These sorts of shifts are often more important on a population level. What they may mean is that some people who are "borderline" for dementia may, if these conditions are not treated effectively, progress to dementia requiring full time care.


What did the authors conclude?

Given most of the risk factors for dementia  -  age, heredity and head trauma -  are beyond the control of the patient or their doctors, finding modifiable risk factors gives some hope to would-be sufferers.

The authors suggested that here was yet another incentive to screen for diabetes and hypertension earlier and treat these conditions aggressively.

Interventions aimed at hypertension or diabetes that begin before age 60 years might lessen the burden of cognitive impairment in later life.

Unfortunately large scale prospective trials of antihypertensive medication or intervention for diabetes in the prevention of Alzheimer's disease and cognitive decline are yet to be undertaken.

In the meantime, the value of early detection and treatment of these diseases to protect cognitive function is still an educated guess.

Knopman D. et al. Cardiovascular risk factors and cognitive decline in middle aged adults. Neurology 2001;56:42-48