For my final post I want to talk about
The correlation between genetics and lifestyle:
Why are asians more susceptable to diabetes than caucasians?
Through the following link you can also view My Statement paper: My Statement Paper
Diabetes, in its many forms, is a global disease that increases the blood glucose levels and therewith brings along many short-term symptoms like polyuria, excessive thirst and weight loss. Long-term complications like heart and kidney failure can occur and eye and nerve damage. People suffering from diabetes lead relatively cumbersome day-to-day lives depending on the severity of the case. They periodically need to administer insulin, monitor their blood glucose and plan meals ahead. Often diabetes is associated with obesity and obesity-related health risks like heart failure and strokes even in both sexes, all ages, all races and all smoking levels (Mokdad et al., 2003). Mexico, the United States, New Zeeland, England and Australia are only a couple of countries with one of the highest global obesity rates (“Obesity – adult prevalence rate – Country Comparison,” 2012). Diabetes in these countries is therefor also more prevalent. Obesity is much less common in Africa and Asia where most of the world’s population lives. However obesity rates are increasing in these continents nonetheless, as is diabetes even more rapidly, particularly in Asian countries. The risk of developing diabetes as an Asian is higher compared to Caucasians at even lower BMI levels (Seidell, 2000). So as the countries with the highest obesity rate are known, you would think that the link could easily be made towards diabetes prevalence as well. However, this does not seem to be relevant when it comes to people from Asian descent.
What is the difference between Asians and Caucasians when it comes to the development of diabetes? Is there an important lifestyle aspect that causes Asians to be at higher risk for the disease?
2 diabetes prevalence among native Asians
While diabetes rates are going up globally every year, Asians countries contribute to about 60% of the total diabetic population. This is a strange phenomenon, as Asian countries are known to have healthier traditional eating habits than Western countries. Their diet is lower in fat yet higher in fiber due to the higher consumption of soy, fresh fish, vegetables, fruit and tea and lower consumption of meat and dairy products. The National Cancer Institute even suggests that these cultural dietary habits are the major factors in cancer prevention in Asian countries with genetics being a secondary factor (Brock, 2006). With that trend in mind, why does this healthy diet not have a positive effect on the prevalence of diabetes for Asians as well?
The risk of developing type 2 diabetes as an Asians is twice as high as anyone in a developed country like the United States for instance (Joslin Diabetes Center, 2014). The rate at which diabetes will occur is expected to go up even further in Asia. Table 1 shows the increase of diabetes in several Asian countries. China and Nepal are two examples of countries where the diabetes rate has gone up remarkably over the last two decades. The astonishing trend here is that the large populations of the rural areas in China, India and Nepal underwent an increase in diabetes incidence. The projection by 2030 is a total of 120,9 million people with diabetes in South Asia alone, which is more than double the amount in Europe and North America (Fig. 1) (Gujral et al., 2013).
Table 1. Prevalence and incidence of type 2 diabetes in Asian countries. (Ramachandran et al., 2012)
Figure 1. Projection number of diabetics in South Asia, North America and Europe by 2030. (Gujral et al., 2013)
2.1 Contributing factors to the rapid increase of diabetes in Asian countries
Since the increase in occurrence of diabetes is happening in such a short timeframe, it cannot be attributed to a genomic phenomenon. The rapid socio-economic growth has not only brought environmental changes to the population but also lifestyle and behavioral changes. The urbanization and rural migration in many Asian countries acts as a major contributing factor towards developing diabetes. Rural-to-urban migrations, usually is pursuit of employment, has many negative effects on the pathogenesis of diabetes; a decrease in physical activity, weight gain due to dietary shift towards high-energy processed foods and more exposure to negative environmental factors (viruses, pollution, …). In almost 30 years, the occurrence of a Chinese adult with diabetes went from 1% to 10% in 2008 in urban areas. But also rural areas are being affected by socio-economic progress. When we look at India as a case study, which is a country with a lot of its population living in rural areas like China and Nepal, we can see in Figure 2 that the occurrence of diabetes increases and the tolerance towards glucose, which is related to diabetes, decreases in rural areas due to lifestyle transitions. Several other reports also show this similar trend in other countries like Thailand, Malaysia and Bangladesh (Ramachandran et al., 2012).
Figure 2. Increasing occurrence of diabetes and impaired glucose tolerance (IGT) in rural populations of India. (Ramachandran et al., 2012)
2.2 Different thresholds against established risk factors
The socio-economic progression and more specifically a high calorie diet and decreased physical activity in these Asian countries causes diabetes rates to increase, but the anatomy, and therefor the genome, of Asians also has its part in the reason for the increasing prevalence of diabetes.
People from Asian descent develop diabetes at an earlier stage in life than western populations. Age seams to be an important contributor for diabetes development in Asian populations. So not only the living environment and geographical locations are relevant to the ethnic differences in the prevalence of diabetes but genetic factors have a rather major role as well. There are numbers to back this statement up; in the 35-44 year age group in China, the occurrence of type 2 diabetes has increased with 88% in merely six years. In India the occurrence increased by 36% in 2006 for people under 44 years. What became apparent is that the effect of age has considerable differences between ethnic groups when it comes to prevalence of diabetes, even at the same BMI (Nakagami et al., 2003).
2.2.2 Body Mass Index
High Body Mass Index (BMI) is often used as an indicator for obesity and therefore diabetes. Despite having lower average body weight, Asians accumulate diabetes a lower BMI levels compared to western populations and even the smallest increments in body weight can potentially already trigger glucose intolerance and consequently type 2 diabetes in genetically predisposed subjects (Chan et al., 2009). BMI can depend on the metabolism of a person too. Despite having a normal BMI, it is possible to still be ‘metabolically’ obese (Yoon et al., 2006). This particular phenotype is characterized by having obesity, less muscle tissue, a higher percentage of body fat and a higher chance of diabetes, yet a normal weight (Shelgikar et al., 1991). It is apparent that there needs to be a modification between the association of BMI and diabetes for different ethnicities as the western model does not apply for Asians. To determine the criteria for diabetes different western and Asian study groups need to be compared.
2.2.3 Abdominal visceral fat
Asian populations accumulate more intra abdominal body fat and on average have lower muscle mass. This gives rise to a higher occurrence of diabetes at possibly lower BMI. A BMI over 23 kg/m2 is considered overweight for Asian populations (Daneman, 2006).The cause for this might be ‘hidden’ fat in the body. Asians appear to have visceral fat between the organs, something Caucasians do not have. This phenomenon affects the amount of secreted leptin and adiponectin (regulating cytokines) and negatively affects the metabolism ultimately leading to diabetes. Adiponectin levels decreases when type 2 diabetes develops and leptin levels increase with increasing BMI (Gujral et al., 2013). Using ELISA to determine the amount of these cytokines and Magnetic Resonance Imaging (MRI) to determine the amount of hidden fat, Japanese women were studied against Caucasian women. The Japanese women had significantly higher amounts of visceral fat and lower BMIs, consistent with low levels of adiponectin and high levels of leptin, yet were twice as likely to have diabetes compared to the Caucasian women (Nainggolan, 2013). In another study, the body fat was studied in Asian-Indians and African-American men. The Asians had up to 30% more body fat compared to African-Americans or Caucasians. The higher levels of body fat and lower levels of muscle mass could explain the higher risk of developing diabetes (Banerji et al., 1999).
Figure 3. relation between body fat and BMI in Asian-Indians and African-American men. (Banerji et al., 1999)
2.2.4 Sleep deprivation
The duration of sleep appears to also play a role in the prevalence of diabetes. The amount of hours is correlated to the amount of appetite-inducing hormone that the body produces. A study conducted on 900 individuals during 5 years, resulted in 16,2% of the subjects developing incidental diabetes. Also disturbances during sleep can have their effect (Gujral et al., 2013).
2.2.5 Tobacco and alcohol
China and India are tobacco-producing countries. The populations therefore often also chew or smoke tobacco, especially in rural areas. It is shown that the risk of developing diabetes rises with 45% in smokers compared to non-smokers. Heavy smokers, who smoke more than 20 cigarettes as day, are at highest risk to develop the disease (Willi et al., 2007).
Also excessive alcohol consumption has a negative effect on the development of diabetes (Nakagami et al., 2003).
3 Diabetes prevalence among Asian Americans
Being Asian makes you genetically predisposed to be at higher risk of type 2 diabetes, even at lower BMI. A real problem occurs when Asians remain undiagnosed due to weight gain not being the tale for diabetes in their case. Of course other symptoms are there, like thirst, polyuria and fatigue but as weight gain is the major telltale for diabetes in western society, Asian Americans often remain undiagnosed (Joslin Diabetes Center, 2014). Migrated Asians Americans have a 10% chance to develop diabetes. This is due to genetic factors but also environmental influences. But environmental factors become more of an issue in the case of Asian Americans, or in any case of Asians migrating to a western society. For instance, Chinese Americans are at higher risk of diabetes than native Chinese populations in rural areas. The same is true for Japanese Americans. This clearly indicates that environment and lifestyle habits are important contributing factors. Interestingly, second or third generation Japanese Americans appear to still be at higher risk for diabetes, even though they are well integrated in the American eating habits and lifestyle. This indicates the genetic factor that cannot be underestimated. For this reason, Asians especially need to monitor their body weight as even the smallest increase in weight increases the risk of developing diabetes sharply. However, the BMI threshold needs to be set according to the ethnicity to be accurate.
Taking it a step further, the risk of diabetes appears to be higher in all the other ethnic groups than Caucasians. Before they are even considered overweight, they could already have developed diabetes, which is usually not the case for Caucasians where obesity is a very important sign of diabetes. Doctors need to know this and stop waiting for Asians to gain weight before taking diabetes test. The most important change they need to undertake is lowering the BMI threshold to 23 kg/m2for Asians. Again taking Indians as a case study, compared to Caucasians, they are diagnosed 10 years earlier and with 5 to 10 units BMI thinner too (Nainggolan, 2013).
The alarming increase of diabetes rates in Asian countries like China, Nepal and India are due to the socio-economic progression that induces a lifestyle transition. The young age at which it can accumulate and the many possible complications it can cause are of significant concern. The urbanization, the decrease in physical activity and the increased consumption of high-calorie processed foods have consequences even more important for Asians than for Caucasians as they have the genetic disadvantage here. Environmental factors stay the same for both, however western populations have had a longer time to adapt to the particular eating habits of the associated countries. It is well worth to talk about an epidemic among Asian populations.
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