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Blood Thickens as You Get Older

Oxidative Stress and Blood Viscosity in Mid-Life and Senior Adults

A staggering 41.4 million Americans (about 1 in 8) were 65 years or older in 2011.1 This represents an 18% increase since the year 2000. Additionally, the number of older Americans is expected to almost double to 79.7 million in 2040.  It is well known that increasing age is associated with development and progression of many chronic conditions such as cardiovascular diseases, arthritis, type II diabetes, glaucoma, dementia, and many more.  Furthermore, the prevalence of chronic illnesses in the United States is expected to increase by 50%  by 2040.2 What if there was one factor that tied many of these chronic conditions together? What if this factor was also shown to increase with age?  Although this seems like wishful thinking, something as simple as the thickness and stickiness of a patient's blood may hold some key answers.

Blood Viscosity and Oxidative Stress

Blood viscosity is a measurement of the blood's resistance to flow.  High blood viscosity impairs the ability of blood to flow freely throughout the body.  Because all living cells depend on blood to supply them with oxygen and nutrients and to dispose of wastes, inadequate blood flow can cause a myriad of problems not only to the cardiovascular system but throughout the human body.  As the body ages, it becomes less able to respond to homeostatic imbalances and becomes inundated with reactive oxygen species (ROS), reactive nitrogen species (RNS), and other free radicals.3 Excess oxidative stress can have detrimental effects on red blood cells (RBCs) by reducing their membrane fluidity, which increases blood viscosity and impairs blood flow.4 Is elevated blood viscosity an early indicator of an age-associated disruption in homeostasis?

A direct positive relationship between whole blood viscosity and age (r = 0.65; p < 0.0001)  was found in a study done by the Gerontology Research Center at the National Institute of Aging.5 The researchers randomly selected 147 subjects from the Baltimore Longitudinal Study of Aging and evaluated age-associated changes in cerebral blood flow determinants and oxidative stress.  While other flow-related measures like plasma viscosity, red cell rigidity, mean cell volume, red cell aggregation, and fibrinogen showed significant linear increases with age, blood viscosity demonstrated an altogether different trend with age.  The relationship between blood viscosity and age remained relatively unchanged, until after age 60, when blood viscosity was shown to increase exponentially with age.  These changes all coincided with age-associated decreases in blood flow and flow velocity as confirmed with Doppler ultrasonography. 

In addition to the findings of age-associated blood viscosity increases, the researchers found increases in oxidative stress as a result of normal aging.  Elevated oxidative stress was suggestive of direct damage to red blood cell membranes and subsequent increases in red cell rigidity, mean cell volume, and aggregation, all contributors to increased blood viscosity.  

A separate study of 154 subjects with varying stages of type-II diabetes, including a healthy control group, patients with prediabetes, diabetes, and diabetes plus cardiovascular disease, showed that the 76% prevalence of oxidative stress among the patients was associated with elevated blood viscosity, as was the 95% prevalence of oxidative stress in the prediabetes group.6

Mitigating the Effects

Age-related cerebral blood flow impairment and oxidative stress can cause decreased oxygen delivery to brain tissues, neuronal damage, and subsequent cognitive impairment.  In an attempt to address these concerns many people take dietary supplements that contain antioxidants and compounds supporting a healthy circulatory system.  No compound for cognitive health is more studied than Ginkgo biloba.  In a study of 48 men aged 60 to 70, those treated with Ginkgo biloba extract showed a reduction in blood viscosity, improved cerebral perfusion, and better global cognitive function after 8 months.7 The control group showed elevated blood viscosity, reduced cerebral perfusion, and cognitive degeneration.  Ginkgo biloba and other natural products such as polyphenols, flavanoids, n-3 fatty acids, resveratrol, and curcumin may provide neuroprotection either by reducing blood viscosity and improving cerebral blood flow, scavenging free radicals and reducing oxidative stress, or by acting through some other mechanism.8

Blood viscosity is an emerging biological parameter that is most closely associated with cardiovascular diseases, but the role of blood viscosity is not limited to any single disease state.  Accumulating evidence has linked blood viscosity to oxidative stress, inflammation, cerebral perfusion, and aging itself–not just cardiovascular health.  New methods for blood viscosity testing make it easy to include as part of laboratory assessments.  Blood viscosity measurements can give valuable insights into various disease states whether they may be a causative pathology or a secondary manifestation of an underlying condition.


References:

1.Administration on Aging (AOA); U.S. Department of Health and Human Services. A Profile of Older Americans: 2012. 2012; http://www.aoa.gov/Aging_Statistics/Profile/2012/docs/2012profile.pdf. Accessed May 15, 2013.

2.Summer L, O'Neill G, Shirey L. Chronic conditions: A challenge for the 21st century: National Academy on an Aging Society; 1999.

3.Finkel T, Holbrook NJ. Oxidants, oxidative stress and the biology of ageing. Nature. 2000;408(6809):239-247.

4.Nwose E, Jelinek H, Richards R, Kerr P. Erythrocyte oxidative stress in clinical management of diabetes and its cardiovascular complications. British Journal of Biomedical Science. 2007;64(1):35-43.

5.Ajmani R, Metter E, Jaykumar R, et al. Hemodynamic changes during aging associated with cerebral blood flow and impaired cognitive function. Neurobiology of Aging. 2000;21(2):257-269.

6.Richards R, Nwose E. Blood viscosity at different stages of diabetes pathogenesis. British Journal of Biomedical Science. 2010;67(2):67.

7.Santos R, Galduroz J, Barbieri A, Castiglioni M, Ytaya L, Bueno O. Cognitive performance, SPECT, and blood viscosity in elderly non-demented people using Ginkgo biloba. Pharmacopsychiatry. 2003;36(4):127-133.

8.Farooqui T, Farooqui AA. Aging: an important factor for the pathogenesis of neurodegenerative diseases. Mechanisms of Ageing and Development. 2009;130(4):203-215.

 

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