19 Sept 2019

Study links nocturnal blood pressure with diabetes and dementia

Dr Chris Karayiannis
by Anne Crawford

Monash University researchers investigating the association between Type 2 diabetes and dementia have found an interesting factor linking the diseases: the dipping of nocturnal blood pressure.

Dr Chris Karayiannis said the Peninsula Clinical School researchers were investigating the poorly understood mechanisms behind the increased risk of cognitive impairment and dementia faced by people with type 2 diabetes.

“This increased risk is long recognised – if we have insight into exactly how it increases the risk of dementia it might help us find targets to prevent this from happening,” Dr Karayiannis said. “Type 2 diabetes could increase the risk of dementia through increasing blood pressure or increasing arterial stiffness, but it could also occur through non-vascular mechanisms like a direct effect of raised blood glucose, or increasing inflammation in the brain.”

The researchers conducted a study of 23 discordant twin pairs – one with, one without type 2 diabetes – recruited through the Australian Twin Registry. The twins, from all around Australia and with a median age of 64 years, were asked to perform various cognitive tests, answer questionnaires, had their waist circumferences measures and underwent various brain scans. They wore a blood pressure monitor for 24 hours.

The study found that the twins with diabetes had poorer cognition in the domain of attention, implying that they may not function as well cognitively. It examined the role of measures of blood pressure, aortic stiffness and haemodynamic measures but did not find an association between type 2 diabetes and most of these measures.

“What I expected was that blood pressure would generally be higher and so would the markers of aortic stiffness – that these would be worse in people with diabetes, but they were similar,” Dr Karayiannis said.

The study did, however, find a connection between diabetes and what’s called nocturnal central systolic dipping – the blood pressure of twins with diabetes didn’t drop or ‘dip’ at night as is usual in most people – and that this reduced dipping was associated with cognitive performance in the twins with diabetes.

“Blood pressure’s supposed to drop by about 10 percent when people are asleep, although it’s not known exactly why,” Dr Karayiannis said. “It is known that if blood pressure doesn’t drop at night the person will have a higher cardiovascular risk.”

One explanation for impaired dipping in type 2 diabetes may be the presence of co-existent sleep apnea, which is known to be associated with nocturnal hypertension, the paper suggested.

Dr Karayiannis said the finding of nocturnal dipping was “hypothesis-generating”.

“It’s an interesting hypothesis because it’s something we don’t routinely look at,” he said. “Abnormal dipping is potentially something that could be treated, if found to be important in cognitive decline in people with type 2 diabetes. We need to reproduce the finding in a larger study.”

Professor Velandai Srikanth was senior author on the study while Dr Chris Moran was instrumental in it.

Professor Srikanth said, “This may be another piece of the puzzle in trying to explain the effects of diabetes on brain health, which is an important issue in the context of reducing the risk of dementia.”

A subsequent, as yet unpublished, study of a large sample of elderly people with diabetes has shown that those with less dipping showed microstructural abnormalities in the white matter of the brain. The preliminary findings of this study, conducted as part of Dr Karayiannis’ PhD and published as an abstract in the Australasian Journal of Alzheimers, were presented at conferences.

Karayiannis C, Moran C, Sharman JE, Beare R, Quinn SJ, Phan TG, Wood AG, Thrift AG, Wang WC, Srikanth V. Blood Pressure, Aortic Stiffness, Hemodynamics, and Cognition in Twin Pairs Discordant for Type 2 Diabetes. J Alzheimers Dis. 2019 Aug 16. doi: 10.3233/JAD-190319. [Epub ahead of print]

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