Tuesday April 12 2011
Wrist size was linked to blood sugar but needs more research
“Big wrists could be a warning of heart danger for your child,” according to the Daily Mail.
The news story is based on an Italian study that assessed whether children’s wrist circumference was associated with their blood sugar and resistance to insulin, the hormone that regulates blood sugar levels. The scientists behind the research suggest that these factors could be used to predict future cardiovascular disease.
While the research did find that wrist size was associated with increased insulin levels and insulin resistance, there are several shortcomings that undermine the link. For example, the children were not followed over time, so it is not possible to say whether having larger wrists as a child does actually increase risk of cardiovascular disease or type 2 diabetes in the future. Also, the study recruited only obese and overweight children, who may have already experienced changes in their body’s ability to regulate sugar and insulin that do not occur in children of ideal weight. In short, from this initial exploration it is not yet clear whether wrist size can be considered a useful predictor of potential health risks.
Where did the story come from?
The study was carried out by researchers from Sapienza University of Rome and was funded by a grant from the Italian Ministry of Education. It was published in the peer-reviewed medical journal Circulation.
The Daily Mail’s headline did not reflect the content of the research, which did not make a direct assessment of cardiovascular risk based on wrist size. However, the researchers did say that one factor being studied (reduced sensitivity to insulin) was associated with subsequent cardiovascular disease. The Daily Mail did appropriately highlight in its report that the research studied only obese or overweight children and that further research would be needed to see whether the findings applied to children of normal weight.
What kind of research was this?
This was a cross-sectional study in a group of children that looked at whether there was an association between wrist size and the ability of the body to respond to insulin. Insulin is the hormone that allows glucose to be taken up from the blood and stored. People who are insensitive to insulin are prone to a build-up of glucose in their blood (hyperglycaemia).
The researchers wanted to see if there was an easily detectable clinical marker of insulin resistance, a factor that could potentially be used to identify children at risk of future cardiovascular disease.
The researchers suggest that several studies have shown that excess circulating insulin in the blood (hyperinsulinaemia) is associated with increased bone mass. They propose that the overall circumference of the wrist could be a good measure of how the bones within have grown in response to insulin levels in the blood, and say that this measure of skeletal frame size is not affected by body fat variation. They, therefore, tested whether there was an association between wrist circumference and insulin resistance.
What did the research involve?
Two groups of overweight and obese children were recruited, the first between September 2008 and September 2009 and the second between August 2010 and November 2010. The participants were on average 10 years of age and, in total, 637 participated.
After fasting in the morning the children had their body weight, height, wrist circumference and body mass index (BMI) measured, as well as blood levels of glucose, insulin, fat and cholesterol. The second group of participants also had their waist circumference measured. From the fasting glucose and insulin levels the researchers were able to estimate insulin sensitivity using a method called the homeostatic model assessment of insulin resistance (HOMA-IR).
To measure the diameter of the wrist bones the researchers used a magnetic resonance imaging (MRI) machine to scan the wrists of 51 of 477 participants, producing a series of cross sections through the depth of the wrist. A radiologist then found anatomically equivalent cross sections in each participant and used these to measure the area of the wrist.
What were the basic results?
The researchers first used a statistical technique called regression to determine how much factors such as fasting insulin, HOMA-IR scores and blood fat levels were associated with wrist size and BMI.
They found that fasting insulin and HOMA-IR scores were associated with both wrist circumference and BMI, but that blood fat was associated with wrist circumference only.
The researchers then looked at the data from the 51 individuals who had MRI measurements taken of their wrists. They were able to measure the wrist bone area and subtract it from the total wrist cross-section area to estimate the wrist adipose tissue (fat).
They found that the bone tissue area, but not the area of fat in the wrist, was associated with insulin levels and their HOMA-IR measure.
In the second group of 160 children the researchers had also measured waist circumference. There was a strong correlation between waist circumference and wrist size, statistically calculated to have an ‘r’ value of 0.75 (a perfect correlation between the two factors would be expressed as an r value of 1).
How did the researchers interpret the results?
The researchers said that their measurement of wrist circumference reflects bone tissue area and “is highly correlated with measures of insulin resistance in a population of overweight/obese children and adolescents”.
They also suggest that measurements of waist circumference in children may be variable owing to sex, ethnicity and variation in how the measurements are performed. They say that wrist circumference is “easily accessible and measurable” and can be assessed with only minimal action from patients. They also say that wrist circumference is more likely to indicate insulin resistance than measures of waist circumference.
This research suggests that a child’s wrist circumference may be a potential measure that doctors could take to help predict risk of insulin resistance. They say that the associations that they found between wrist circumference and insulin resistance measures are based on a difference in bone area rather than amount of wrist fat. However, there are several limitations to this research, and further work is needed to validate these findings:
- This was a cross-sectional study, meaning that measurements were taken at one time only. It is, therefore, not possible to assess how the insulin system and any poor regulation of blood sugar affected bone growth over time in these children.
- The participants were all classified as overweight or obese, but the study did not assess the point in their childhood at which they had gained weight. A child who had gained weight early on in life may have experienced a different effect on their bone development to a child who had only recently experienced rapid weight gain.
- The actual measurements of glucose and insulin levels and insulin resistance were not reported in the research paper. It is, therefore, not clear whether the children already had clinically relevant insulin insensitivity or particularly high insulin and glucose levels, and whether these would constitute clinically defined glucose intolerance or type 2 diabetes.
- It is not clear whether these findings would have any relevance for children who aren’t obese or overweight.
- The researchers did not measure whether participants with large bone area also had larger fat deposits on their wrists. They estimated fat deposits on the wrists by subtracting the cross-sectional bone area from the total cross-sectional area. This does not take into account other tissue contained within the wrist, for example, muscles and tendons. The researchers also didn’t measure the variability in the amount of fat deposited at the wrists across the study population. Such assessments would be needed to determine whether wrist circumference is determined by bone area.
- The wrist bone measurements were taken in a relatively small group. Follow-up in a larger sample would be required to validate the reported findings.
- The researchers stated that the aim of the current study was “to find an easy way to detect clinical marker of insulin resistance which can be used to identify young subjects at increased risk of cardiovascular disease”. Again, as this was a cross-sectional study, the participants were not followed over time. This study did not assess whether children and adolescents with wrists of larger circumference had an increased risk of subsequently developing cardiovascular disease or type 2 diabetes.
- It is a relatively simple process to assess blood sugar levels and insulin levels by performing blood tests. While measuring wrist circumference would be slightly easier, the method is not likely to be as accurate and results would probably need to be confirmed by subsequent blood tests. This begs the question of how much benefit wrist circumference would have as an independent measurement.