Atherosclerosis and Particulate Matter's Effects on Human Health

Arteriosclerosis is a condition that occurs when the blood vessels that carry oxygen and nutrients from your heart to the rest of your body which are also known as arteries become thick and stiff. This sometimes restricts blood flow to organs and tissues. When the arteries stiffen and harden as opposed to flexible and elastic as they are supposed to be, it is referred to as atherosclerosis which is a specific type of arteriosclerosis. Atherosclerosis refers to the buildup of fats, cholesterol and other substances in and on your artery walls (plaque), these plaques can burst, triggering a blood clot. Although atherosclerosis is often considered a heart problem, it can affect arteries anywhere in your body. Atherosclerosis may be preventable and is treatable however, it is the cause of about 50% of all deaths in westernized society. (cite)

Over time, there have been various studies that establish an association between ambient air pollution and cardiovascular mortality and morbidity. Ambient air pollution is defined by the World Health Organization as potentially harmful pollutants emitted by industries, households, cars, and trucks. Of all of these pollutants, fine particulate matter has the greatest effect on human health. However, these studies focus on the later stages of this disease and not on the preclinical conditions hence, these preclinical conditions are barely understood. In this study, it was hypothesized that current levels of these ambient particulate matters which are up to 2.5mm may contribute to atherosclerosis which is a major causative factor for cardiovascular morbidity and mortality. This study was carried out on animals and the hypothesis was supported. To conduct this study in humans, researchers measured the association between residential ambient and CIMT which is carotid artery intima-media thickness which is a quantitative measurement tool that investigates the contribution of long-term exposures to subclinical stages of atherosclerosis at any age.

This study was carried out in Los Angeles, California using baseline data from two controlled clinical trials. These trials were conducted by the University of Southern California. One of the studies was the Vitamin E Atherosclerosis Progression Study (VEAPS) and the B-Vitamin Atherosclerosis Intervention Trial (BVAIT). VEAPS looked at the effects of vitamin E on the progression of atherosclerosis it included 353 participants. These participants were above 40 years of age. They included men and women with slightly increased LDL cholesterol. Participants for this study were excluded based on high alcohol intake, and life-threatening diseases. BVAIT focused on the effect of vitamin B supplements on the progression of atherosclerosis. It included 506 participants who were over the age of 40 as well. Women had to be postmenopausal and had to be stroke, cancer, or heart disease-free. Participants were excluded on the same basis as the VEAPS study. In total, 859 patients were involved and 58 were excluded because they did not reside in the area required for the study which was areas with data.

Ultrasounds were performed on the right common carotid artery before the intervention and this was done because the researchers used this as the outcome. Participants were also asked to complete a survey that assessed the major risk factors for CVD. The risk factors included were diet, physical activity, smoking history, and vitamin supplements. To measure the lipid concentrations, fasting blood samples were drawn. Exposure was assessed using a novel approach that was derived from a GIS system and geostatistics which helps in assessing long-term mean ambient concentrations. (cite)This was used to capture the residential address of the participants. The residential address was used as opposed to working places although there are also sources of exposure because studies show that people spend most of their time indoors.

The statistical analysis to test the variative association between CIMT and ambient was done using a linear regression model as well as weighted least- square models. The model was then expanded using covariates that were associated with or CIMT. These models were implemented on the universal kriging estimate. The general analysis approach was conservative. This was necessary because it helped the researchers test the sensitivity of the effects. Stratification was also done by sex, age, smoking status, and lipid-lowering drug therapy. The researchers also took into account factors such as diet, education, blood pressure, and income. (cite smaller article)

The results suggested that age was the only covariate that had a significant effect on the point estimate. This made sense because there were age-related modifications done in the study. Apart from age-related modifications, there was also hormone replacement therapy adjustment for women. In the study, 109 participants that reported lipid-lowering medication at the start of the study showed stronger associations between CIMT and regardless of sex. In terms of differences based on sex, women in older age groups more specifically women older than 60 showed larger effects. The effect of smoking was not significant.

There was thickening of the carotid artery by about 4% for every 10 micrograms per cubic meter increase of fine particles. Participants that were more exposed had an increased artery thickening by 8%. As stated earlier, women older than 60 experienced more effects with a thickening of about 15%. This can be as a result of women having smaller activity spaces than men as well as older age groups spending more time in the home. 64% of men were undergoing lipid-lowering therapy which was an indicator for risk profiles prone to atherogenesis. The study also showed that risk factors such as diabetes could increase susceptibility to ambient particulate matter. The results of this study support the hypothesis that was proposed by the researchers. There is a biologically plausible link between long-term air pollution and increased atherosclerosis which ultimately leads to cardiovascular mortality.

Biases of the study was also a major focus of the paper. One of them was the sample of participants that were used in the study. Although they were already part of a clinical trial before this study, it limits the generalization of the study to other populations. Apart from age, they were other possible uncontrolled or residual confounding that could affect the results. There were other observed modifications of associations but these could not be fully understood because of the reduced sample size, the recruitment process of volunteers and the nature of the data.

Limitations to this study were seen in the exposure assignment which can affect the results by biasing it towards weaker associations. Another limit is related to the difficulty to interpret or generalize the results because the studied population is very different from the population treated in normal life.

In conclusion, because this is the first study of its kind, there are various aspects of the study that require further investigations to establish credible results to support this study. To determine whether air pollution has an effect I atherosclerosis after a certain age needs further investigation. Also, the researchers suggested these researches should be directed at identifying factors that determine susceptibility to, investigate the effect of air pollution on the progression of CIMT in susceptible groups.