Metabolic Syndrome and Cognitive Decline

The metabolic syndrome is a group of risk factors for cardiovascular disease, including high blood pressure, impaired levels of blood cholesterol, altered glucose metabolism or insulin resistance, and obesity. These risk factors together increase the likelihood of heart disease, stroke, peripheral vascular disease, and type 2 diabetes. Now, a new study concludes that women with metabolic syndrome are also at an increased risk for dementia and cognitive dysfunction.

The study, published in a recent issue of Archives of Neurology, reports findings of a 4-year prospective study of nearly 5000 postmenopausal women in 25 countries. The study initially examined women with osteoporosis, but an ancillary study examined cognitive function in the study subjects. The women were screened for the components of the metabolic syndrome at baseline, and 10% of the women were diagnosed with the condition. Nearly all women were diagnosed with at least one component of the syndrome. All of the women were also screened for cognitive impairment at baseline, based on a combination of clinical diagnosis and standard neuropsychiatric evaluations, then yearly for 4 years. At baseline, no women showed signs of cognitive dysfunction.

Of the original 497 women diagnosed with metabolic syndrome, 7.2% developed cognitive impairment over the course of the study. Only 4.1% of women without metabolic syndrome developed cognitive impairment. Overall, there was a 23% increased risk of developing cognitive impairment per increase in component of metabolic syndrome. Of the components of metabolic syndrome, high fasting glucose levels or diabetes were associated with the most significant risk of cognitive impairment.

The mechanism by which metabolic syndrome increases cognitive dysfunction has not been clearly defined, and was not examined in this current study, but several previous studies have suggested that insulin resistance may increase the accumulation of beta-amyloid plaques that contribute to dementia. Further, obesity has been associated with brain atrophy and the degradation of neurons. Interestingly, type 1 diabetes — not usually associated with obesity or the metabolic syndrome — has also been associated with decreased cognitive function, indicating that chronic hyperglycermia and hyperinsulinemia might be to blame for decreased executive functions, cognitive impairment, and dementia. Type 1 diabetes has been shown to decrease mental speed and flexibility, while type 2 diabetes is additionally associated with changes in learning and memory.

Age may play a role in metabolic syndrome and its associated risk factors. Namely, the oldest groups of people studied seem not to experience cognitive decline at the same rate as younger subjects with metabolic syndrome. In a study of 599 people aged 85 and older with metabolic syndrome, cognitive decline actually slowed from 85 to 90 years old, compared to an accelerated decline in people with metabolic syndrome up to age 75. Some researchers argue that metabolic syndrome is less significant in the oldest of the old.

Numerous risk factors collectively influence cognitive function over a lifetime. Some occur early in life, such as education, or are unalterable, such as family history or genetic predisposition. Other risk factors, however, appear to controllable and modifiable, such as the components of the metabolic syndrome. Most of these components can be treated and managed with lifestyle modifications, and the earlier people address the risk factors and alter their behaviors, the earlier they can reduce the risk of developing any number of serious medical complications. While many studies agree that the components of metabolic syndrome are associated with decreased cognitive function, more studies need to be conducted to explain the mechanism behind this association. But, for now, people worldwide should take this information to heart (and mind) and curtail the growing prevalence of obesity, high cholesterol, high blood pressure, and diabetes. As if anyone needed one more reason.

References

BIESSELS, G., STAEKENBORG, S., BRUNNER, E., BRAYNE, C., & SCHELTENS, P. (2006). Risk of dementia in diabetes mellitus: a systematic review The Lancet Neurology, 5 (1), 64-74 DOI: 10.1016/S1474-4422(05)70284-2

van den Berg, E., Biessels, G., de Craen, A., Gussekloo, J., & Westendorp, R. (2007). The metabolic syndrome is associated with decelerated cognitive decline in the oldest old Neurology, 69 (10), 979-985 DOI: 10.1212/01.wnl.0000271381.30143.75

Xiong, G., Plassman, B., Helms, M., & Steffens, D. (2006). Vascular risk factors and cognitive decline among elderly male twins Neurology, 67 (9), 1586-1591 DOI: 10.1212/01.wnl.0000242730.44003.1d

Yaffe, K., Weston, A., Blackwell, T., & Krueger, K. (2009). The Metabolic Syndrome and Development of Cognitive Impairment Among Older Women Archives of Neurology, 66 (3), 324-328 DOI: 10.1001/archneurol.2008.566