Stroke Afflicted Residents Near Pollution Sites in New York, USA
Pollution produces causes of stroke among residents near pollution sites in New York
Is stroke induced by hazardous wastes?
Exposure to persistent organic pollutants (POPs) may lead to high cholesterol in the blood stream, and increase risk of atherosclerosis with embolism that results in stroke.
Medical researchers “tested the hypothesis that exposure to contaminants from residence near hazardous waste sites in New York State influences the occurrence of stroke.”
“Results -: After adjustment for age and race, the hospitalization rate for stroke in zip codes with POPs-contaminated sites was 15% higher than in zip codes without any documented hazardous waste sites...as compared to zip codes without an identified waste site” (Ivan Shcherbatykh, Xiaoyu Huang, Lawrence Lessner and David O Carpenter. Hazardous waste sites and stroke in New York State Environmental Health: A Global Access Science Source 2005, 4:18 http://www.ehjournal.net/content)
Researchers concluded that “results suggest that living near a source of POPs contamination constitutes a risk of exposure and an increased risk of acquiring cerebrovascular disease. However further research with better control of individual risk factors and direct measurement of exposure is necessary for providing additional support for this hypothesis.”
Data used were records “for 1993–2000 from the New York Statewide Planning and Research Cooperative System (SPARCS) database,” including diagnoses upon discharge for patients admitted in state hospitals.
“The rates of stroke hospital discharges were compared among residents of zip codes containing hazardous waste sites with POPs, other pollutants or without any waste sites “
"POPs are chlorinated organic compounds [polychlorinated biphenyls (PCBs), dioxins and chlorinated pesticides] that are resistant to degradation and able to bio-accumulate in fatty tissues of living organisms. These compounds are semivolatile, and present in the atmosphere as vapors or adsorbed on suspended particles . Multiple adverse health effects have been associated with the exposure to POPs [7,8] including cardiovascular pathologies, such as hypertension, ischemic heart disease, and atherosclerosis [9-11]."
"One mechanism linking exposure to POPs and cardiovascular diseases may be through increased serum lipids, a known risk factor for atherosclerosis. Serum lipids , plasma triglyceride levels , and total cholesterol are elevated in dioxin and PCB-exposed populations. Dioxin and coplanar PCBs cause the production of reactive oxygen species which, in turn,cause damage to endothelial cells and promote the formation of foam cells and atherosclerotic plaques . The combination of elevated serum lipids in the presence of damaged endothelial cells would contribute to the risk of development of cardiovascular pathology and cerebrovascular disease, especially ischemic stroke. Indeed, our results ...show a stronger relation with ischemic than hemorrhagic stroke." The researchers reported.
Discussions of the above mentioned study ends here. What follows is my interpretation of the study
The study elaborated risk factors like serum lipids, plasma triglycerides and total cholesterol. However, these risk factors are not the ultimate causes of stroke or cardiovascular disease. “Risk factor” and “cause” are not clearly defined or used mutually exclusively in the above technical report.
Let us trace the chain from the ultimate cause to risk factors then to occurrence of stroke.
The researchers mentioned only reactive oxygen species (ROS). However, ROS are derivatives of more fundamental elements that are free radicals. These are molecular oxygen, singlet oxygen and ozone. (A free radical is an atom, or molecule or fragment of a molecular with at least one unpaired electron in its outermost orbital. This unpaired electron is unstable and to stabilize grabs another electron.) Molecular oxygen is used in metabolism, for example, that produce superoxide as by-product. There are other producers of superoxide like nitric oxidase. xanthine oxidase, cyclooxygenase and NADH. Superoxide dismutase, an enzyme, attaches one electron and one hydrogen atom to superoxide and produce hydrogen peroxide, which is a ROS. A ROS acts like a free radical. Superoxide reacts with nitric oxide and produces peroxynitrite, another ROS. Superoxide reacting with another superoxide in the presence of iron produces hydroxyl radical, another ROS. Superoxide reacting with another superoxide in the presence of copper produces alkoxy radical, another ROS. Molecular oxygen or superoxide oxidizes the low density lipoprotein of cholesterol and produces a lipid-oxy, another ROS (Sharma, H. MD. Freedom from Disease. 1993).
Chlorinated organic compounds are other forms of ROS. They have at least one unpaired electron on the chlorine side that grab another electron from another molecule of a tissue. Such grabbing is an injury that results in mutation then tumor or cancer.
Electron grabbing characterizes free radicals and ROS. If one or several electrons were grabbed from cells of the endothelium, the endothelium is injured. (Endothelium is a one-cell layer of the inside wall of arteries.) This injury results in a benign tumor called atheroma (Cranton, E. MD. Bypassing Bypass. Updated second edition.1995). Such injury can occur in aorta or in arteries of the heart. The body attempts to repair this injury with collagen, elastin, cholesterol, fibrin, and calcium. But this attempt at repair goes awry. The repair materials pile on each other and grow into a mound then plaque. This plaque grows further with addition of materials like cholesterol. Macrophages, components of the immune system, engulf lipid-oxy resulting in a foamy material that cling to the walls of the artery that adds to the plaque.
A plaque in the heart arteries or in the aorta may result in stroke. This is of two major kinds: ischemic and hemorrhagic. In ischemic stroke the aorta or heart arteries are narrowed by the plaque resulting in inadequate supply of blood to the brain. The brain cells starved for oxygen die or are disabled. In hemorrhagic stroke, there is rapture of major or small arteries in the brain resulting in bleeding at the surface of the brain or inside it.
The body produces its own free radicals and ROS, the environment contributes free radicals and ROS.
The researchers must be given credit for mentioning ROS as causes of stroke. Other researchers only mention risk factors who sometimes equate risk factors with causes. Risk factors of stroke are age, hypertension, diabetes, cholesterol and smoking. A risk factor is only a device used to predict the probability that a person will contract a disease. Put another way, they exacerbate the effects of the causes of stroke.
The chain of events: causes (free radicals, reactive oxygen species), risk factors (age, gender, cholesterol, diabetes, hypertension, smoking), stroke.