Thursday April 9 2015
Being short may lead to an increase in cholesterol levels
"Shorter people at greater risk of heart disease, new research finds," reports The Guardian.
It reports that a study of nearly 200,000 people has found that for every 2.5 inches (6.35cm) less in height, there is a 13.5% increased risk of coronary heart disease or CHD (also known as coronary artery disease).
This means that someone who is 5ft (1.52m) would have a 32% increased risk of CHD compared to someone who is 5ft 6 (1.71m).
Previous research identified the link between shorter adult height and increased risk of CHD but why this might be was not known. It is thought that environmental factors could be involved. For example a person fed a poor diet in childhood could grow up both shorter than average and unhealthy.
This current study attempted to create a clearer picture by looking for genetic variations linked to short stature that were also linked to CHD.
Through sophisticated statistical analysis they measured the association between shorter height due to these variants and CHD. Oddly there was no association for women.
It should be noted that this type of study can indicate potential reasons for the associations (such as shortness being associated with high cholesterol) but cannot prove that shorter height directly causes CHD.
While you can put on a pair of "killer" or Cuban heels, there is not much you can do about your genetics. Ways you can reduce your CHD risk include stopping smoking, drinking alcohol in moderation and maintaining a healthy weight through diet and exercise. These steps should help keep your cholesterol and blood pressure at a healthy rate.
Where did the story come from?
The study was carried out by researchers from the University of Leicester, the University of Cambridge and numerous other institutes and universities across the UK and internationally. It was funded by the British Heart Foundation, the UK National Institute for Health Research, the European Union and the Leducq Foundation.
The study was published in the peer-reviewed The New England Journal of Medicine.
The UK media accurately reported the study. The Guardian helpfully put the results of the study into context with a quote from one of the authors, Sir Nilesh Samani who said: "The findings are relative, so a tall person who smokes will very likely be at much higher risk of heart disease than somebody who is smaller". He was then quoted by the BBC News as saying: "In the context of major risk factors this [short stature] is small – smoking increases the risk by 200-300% – but it is not trivial."
What kind of research was this?
This was a case control study which compared genetic make-up of people with and without coronary heart disease (CHD). It specifically looked at genetic variations associated with height, and aimed to see if there was an association between ‘genetically determined height’ and risk of CHD. They also studied whether genetically determined height was associated with cardiovascular risk factors.
Previous research identified the link between shorter adult height and increased risk of CHD but the exact reason why was not known. This type of study investigates whether genetics could be a potential reason for the association, but cannot prove that shorter height causes CHD, or rule out other factors contributing to the association.
What did the research involve?
The researchers compared genetic variations that are associated with height in people with and without CHD.
The researchers used data on 65,066 people who had CHD (cases) and 128,383 people with no history of CHD (controls) that had been collected from a number of different studies, and pooled in a previous meta-analysis. This meta-analysis identified 180 DNA sequence variations that were estimated to account for 10% of the difference in people’s heights.
In the current study they measured the association between each DNA variant and height. They then measured the association between each DNA variant and CHD. From this, they calculated whether there was an association between height determined by each DNA variant and CHD. As this association was very small for each DNA variant, the researchers then combined all of the DNA variant results to obtain an overall association for what they termed "genetically determined height" and risk of CHD. They performed separate analyses for men and women.
The researchers then looked for any associations between the genetically determined height and the following risk factors for CHD:
- high blood pressure
- high LDL "bad" cholesterol
- low HDL "good" cholesterol
- high triglyceride level (a type of fat)
- type 2 diabetes
- increased body mass index (BMI)
- high blood sugar
- low insulin sensitivity
What were the basic results?
The average age of participants was 57.3 years and the majority of cases were male (73.8%) compared to only half of the controls (49.8%).
Most of the 180 individual genetic variants that have been associated with height had no statistically significant association with the risk of CHD. The researchers had expected this, as each variant is associated with only a very small effect.
When all of the results were combined, for each 6.5cm decrease in "genetically determined height" there was a 13.5% increased risk of CHD (95% confidence interval (CI) 5.4% to 22.1%).
When looking at men and women separately, there was an association in men, but no significant association between the genetically determined height and CHD in women.
Among the risk factors for CHD, the height-related variants were only associated with LDL (bad) cholesterol and high triglyceride levels. They estimated that 19% of the association between shorter height and CHD could be accounted for by high LDL cholesterol and 12% by high triglycerides.
How did the researchers interpret the results?
The researchers concluded that using a genetic approach there is "an association between genetically determined shorter height and an increased risk of CHD". They suggest that this may in part be due to "the association between shorter height and an adverse lipid profile [levels of total cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, and the calculated low-density lipoprotein (LDL) cholesterol.]".
Previous observational studies have suggested a link between shorter height and CHD. What was not clear was the extent to which this might be due to genetic factors or confounding by socioeconomic and lifestyle factors.
The current study aimed to assess the potential role of genetics, and reduce the possibility of socioeconomic factors influencing the results. To do this the researchers calculated the association between "genetically determined height" and CHD, using 180 genetic variations previously found to be associated with height in Europeans. This reduces the influence of socioeconomic factors as genetic variations are present from birth.
They found an association between genetically determined shorter height and increased risk of CHD. They also found that the genetic variants were associated with high LDL cholesterol and triglycerides and this could at least partly account for the increased risk of CHD. It remains unclear exactly how the genetic variants identified influence cholesterol, triglycerides or CHD. It is also not known if the results would be applicable to people not of European descent.
Interestingly, there was no significant association for women. The researchers say this could be because there were too few women with CHD in the analysis.
Though the study design aims to reduce the possibility of confounding, the researchers note that they cannot rule out the possibility of different behaviours in shorter people having an impact on the results. The study also does not completely rule out other factors influencing the overall link between height and CHD.
Whatever your height you should remain vigilant about the risk of CHD, which has now become the leading killer in the UK.
You cannot change your genetics, but factors that you can control to reduce the risk of CHD include stopping smoking, drinking alcohol in moderation and maintaining a healthy weight through diet and exercise. These steps should help keep your cholesterol and blood pressure at a healthy rate.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.