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Research Article Review: What is the link between ethnicity, weight and the mortality risk of CVD?

Updated: May 7, 2022

Research Article Review: Ethnicity-specific association of BMI levels at diagnosis of type 2 diabetes with cardiovascular disease and all-cause mortality risk

We often associate obesity with a lot of things: serious health complications, various ailments, reduced physical performance, and in extreme cases, even death. But a new study has found that people with higher body fat content are at a lower risk of dying from a heart-related disease than those with lower body fat content. Pretty counterintuitive, huh? Now you may ask what is the underlying mechanism behind this? The study we are about to explore has a strong reason to suggest that ethnicity might play a role in this strange paradox.

The focus of the study was to explore the association between ethnicity, weight(body mass index), and the mortality risk of cardiovascular(CVD) diseases. The study has indicated that research on the association between CVD and ethnicity has been done, but not specifically on how body mass index(BMI) influences their relationship. Before we delve into the depths of this study, it’s important to clearly define the variables of this study and outline their role in its objective. The first variable ethnicity is defined as a group of people that share a common racial and cultural identity. The second variable, BMI, is defined as a value relating the mass, or weight, of an individual, to their height. According to the CDC, a normal person’s BMI falls between the range 18.5 to 24.9. In other words, if your BMI is below 18.5, you would be considered underweight and if your BMI falls above the range, you would be considered overweight. The third variable, CVD, is an abbreviation for cardiovascular disease, commonly associated with high adiposity levels, or high body fat content.

Previous studies have suggested that despite its counterintuitive nature, there may be an inverse relationship between BMI and the risk of death in Type II diabetes patients. This is known as the obesity paradox. In other words, as BMI decreases, the risk of CVD related death increases and vice versa. However, this study will explore the role of ethnicity in this dynamic relationship and to what extent it influences the correlation between the two.

This study suggests a positive correlation between ethnicity and the supposed inverse relationship between the risk of CVD related death and BMI.

The subjects of this study were 51,455 Type II diabetes(T2DM) patients between the ages of 18-70 who identified as either White European, African, Caribbean, or South Asian. It is also important to note that these subjects had no history of CVD or other related diseases at the time of diagnosis. Furthermore, those who were diagnosed with Type I diabetes(TDM1) or gestational diabetes were excluded from this study. In addition, the study did not account for those with a disease history at the time of diagnosis(of Type II diabetes) and those who racially identified as Middle Eastern or Mixed.

Since this study was purely observational, none of the subjects were treated with any experimental drugs or medication. The subjects were grouped based on weight status(BMI) and ethnicity. The subjects were either identified as White European, African Caribbean, or South Asian. The BMI categories were as follows: normal weight, overweight and obese.

The only control factor in this study was sex. All the subjects identified as male. The study also took into account factors such as weight change pattern before diagnosis(of T2DM), age at diagnosis, smoking status, and the incidence of diseases, such as cancer and renal diseases, after diagnosis(of T2DM).

Statistical analyses were performed using STATA version 15 MP, at a two-tailed α level of 0.05.

So did ethnicity play a role in this strange paradox after all? Here are the results:

Basic Demographic(age, sex, race) and Clinical Characteristics:

  1. South Asians(SA) were diagnosed with T2DM at a younger age(47) than African Carribeans(AC) or White Europeans(WE). They also had a lower BMI compared to ACs and WEs.

  2. There were more smokers(current and ex) in the WE group than the other two groups.

  3. There were more normal and overweight patients in the AC group than the SA or WE group at the time of diagnosis.

  4. Across all three BMI categories, normal, overweight, and obese, ACs had similar levels of ever-smokers, current and ex.

  5. There were more smokers among the normal weight SAs than the overweight or obese SAs.

  6. In the WE group, there were more smokers in the normal weight group than the obese group.

  7. The number of normal patients that lost weight before diagnosis was double the number of obese patients that lost weight before diagnosis. This trend was consistent across all three ethnic groups.

CVD and Mortality Risk

  1. Among WEs, there were more CVD events in normal weight patients than obese patients. (Examples of CVD events are heart attacks and strokes.) These events were not related to weight change patterns before diagnosis.

  2. CVD event rates were higher in normal weight WEs than normal weight ACs, but similar to normal weight SAs.

  3. Mortality, or death, rates were significantly higher among normal weight WEs than obese WEs. (This result also had nothing to do with weight change patterns before diagnosis.)

  4. Death rates among normal weight WEs were three times greater than normal weight ACs and SAs.

Association of BMI categories with survival time for CVD and mortality

  1. Normal weight WEs developed CVD significantly earlier(by .5 years) than obese WEs.

  2. There was no significant difference between overweight WEs and obese WEs in terms of the time it took for the first CVD event to occur.

  3. Overweight ACs developed CVDs (about 1.2 years) later compared to obese ACs.

  4. The mean time to death for obese WEs was 7.0 years(after diagnosis) and 7.3 years for obese SAs. Those with normal weight were significantly more likely to die earlier(by .6 years)

As we all know, BMI, weight patterns, and risk of CVD are all inherently linked to each other, but this study supports the claim there might be an inverse relationship between the two as suggested by previous studies. In other words, it supports the hypothesis that lower BMI tends to correlate with a higher risk of contracting a CVD.(To note: in this case, contracting a CVD does not necessarily mean that the patient faces a higher risk of death. It just means they are more likely to get diagnosed with the disease.) However, this conclusion only applies to the WE group. Nonetheless, the same study suggests that normal weight White Europeans and South Asians are at a higher risk of actually dying from a CVD than their obese counterparts. Surprisingly, it seems that the African Caribbean group did not display a significant correlation between BMI and an increased risk of death or CVD.

According to the CDC, one in four deaths related to CVD is caused by smoking. So it should come as no surprise that the group that has a higher risk of CVD also has the highest number of current smokers. In this study, the group with the highest proportion of current smokers was the normal weight WEs. This same group also faced a higher risk of being diagnosed with a CVD.

When assessing the results of a study, it is important to take into account any limitations that might impact its scope. One very common limitation is sample size. In this study, the availability of data was limited because the database from which it was obtained was missing a lot of key information like disease history at diagnosis, death dates, and ethnicity. For this reason, the study had to exclude some of the patients listed in the record. There is also a question of accuracy and completeness of the data that was not excluded.

Well, if there’s one thing this study holds true to, it’s the interesting dynamics between weight pattern(BMI) and death in CVD patients, especially those with TD2M. Although this study does confirm the inverse relationship between the two, what about ethnicity? Could ethnicity truly be the answer to this complex riddle? Well, it is definitely a possibility and a segue into recommendations for future studies. But for now, let’s continue to remind ourselves of the risks and dangers of obesity and other cardiometabolic diseases and remember to maintain a healthy and balanced diet.

by Rida Khan

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