Hypertension, raised blood pressure, is an important mediating mechanism in aging. It is caused by forms of low-level biochemical damage in and around the cells of blood vessel walls, and produces structural damage to organs and the cardiovascular system, leading to dysfunction and death. Hypertension is sufficiently harmful in and of itself that present methods of reducing blood pressure can reduce risk of mortality and clinical age-related disease, even given significant side-effects, and even given that none of these methods address the root causes of hypertension. They override reactions to damage rather than repairing damage. Repair of that damage, once implemented, should prove far more effective.
One of the ways in which hypertension damages organs is through an increased pace of rupture in capillaries and other forms of small-scale structural damage. This is particularly important in the brain, as it has only a very limited capacity to heal injuries of this nature. Cognitive decline driven by hypertension is in part a progression of tiny, unnoticed strokes, each destroying the function of a minuscule portion of the brain. Over time that adds up, and thus we might expect to observe correlations between hypertension and dementia. Nothing is simple in human data, of course, as even straightforward relationships can be challenging to extract from the very noisy data.
Hypertension is a highly prevalent condition, occurring in one-third of the world's adults and in two-thirds of adults over 65 years of age. Both hypertension and dementia are age-related comorbidities which may induce considerable disabilities. Some epidemiological studies showed that hypertension is an important risk factor of dementia, which was evident from the positive relationship between blood pressure at midlife and the subsequently higher risk of cognitive impairment or dementia late in life; however, some other studies provided contradictory evidence that low blood pressure was a risk factor for dementia and cognitive decline.
We, therefore, intend to explore the association between blood pressure and cognition. Data were drawn from 3,327 participants at the baseline of Shanghai Aging Study. History of hypertension was inquired and confirmed from participants' medical records. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured in the early morning. Participants were diagnosed with "cognitive normal," "mild cognitive impairment (MCI)," or "dementia" by neurologists. Multivariate logistic regression was used to evaluate the association between history of hypertension, duration of hypertension, SBP, DBP, or classification of blood pressure and cognitive function.
Our study indicated that history of hypertension, duration of hypertension, and high blood pressure were positively associated with dementia. A significantly higher proportion of hypertension [76.5%] was found in participants with dementia than in those with MCI [59.3%] and cognitive normal [51.1%]. Participants with dementia had significantly higher SBP [157.6 mmHg] than those with MCI [149.0 mmHg] and cognitive normal [143.7 mmHg]. After adjusting for sex, age, education, living alone, body mass index, anxiety, depression, heart disease, diabetes, and stroke, the likelihood of having dementia was positively associated with history of hypertension (odds ratio = 2.10), duration of hypertension (odds ratio = 1.02 per increment year), higher SBP (odds ratio = 1.14 per increment of 10 mmHg), higher DBP (odds ratio = 1.22 per increment of 10 mmHg), moderate hypertension (odds ratio = 2.09), or severe hypertension (odds ratio = 2.45).