Tuesday December 18 2007
Leg length is subject to a number of factors
"Women with shorter legs may have an increased risk of liver disease", the BBC News website reported today. It continued that a study in 60 to 79-year-old women found that those with shorter legs had higher levels of certain liver enzymes and raised levels of the enzymes can indicate a liver that has been damaged or is not working well.
The authors of the study are reported as speculating that their findings were “linked to upbringing”, and in particular to the diet the women ate as children. Alternatively, they suggest that "greater height may boost the size of the liver, which may decrease enzyme levels so ensuring that the liver is able to withstand chemical onslaught more effectively".
The news reports are based on an analysis of data collected from a study of 4,000 British women. In this analysis, the researchers used adult leg length as an indicator of childhood nutrition. However, leg length is influenced by a number of factors including genes inherited from parents. It should also be noted that the levels of four liver enzymes were used as an indirect measure of liver function and damage, but these can also be affected by a large number of other factors, including medication and alcohol consumption.
Despite the newspaper reports, it cannot be said for certain that childhood nutrition (as reflected by leg length) affects liver function or the risk of liver damage as an adult.
Where did the story come from?
Dr Abigail Fraser and colleagues from the University of Bristol and the London School of Hygiene and Tropical Medicine carried out the research. No funding is listed for this study, but the original study from which the data were collected was paid for by the UK Department of Health and the British Heart Foundation. The authors of the study were supported by grants from the University of Bristol and the UK Department of Health.
The study was published in the peer-reviewed Journal of Epidemiology and Community Health.
What kind of scientific study was this?
This cross-sectional study looked at the association between adult leg length - an indicator of childhood nutritional status - and liver damage in women. The study used data collected in the British Women’s Health and Heart Study, which enrolled a random sample of 4,286 women aged 60 to 79 years old, selected from 23 British towns between 1999 and 2001.
The researchers worked out the length of the participants “trunk height” by asking them to sit on a stool and measuring from the stool to the top of their heads. The length of their legs was worked out by subtracting the trunk height from their overall height. The researchers also measured waist and hip size, and recorded details of their backgrounds, health, and medical history.
Levels of four different liver enzymes (called ALT, GGT, AST and ALP) in the blood were measured - high levels of which are linked to liver damage.
Researchers in the current study took this data, available for 3,624 women, and looked to see whether there was any association between the women’s leg and trunk length and the levels of liver enzymes. These analyses took into account the women’s age, and other factors that might affect the results, such as smoking, social class during childhood and adulthood, alcohol consumption, physical activity, and waist to hip ratio. The analyses of woman’s leg length also took into account trunk length, and analyses of the trunk length also took into account leg length.
What were the results of the study?
Women with longer legs had lower levels of three of the four liver enzymes tested (ALT, GGT, ALP). This association remained even when the researchers adjusted for alcohol consumption, social class during childhood and adulthood, smoking, physical activity, trunk length, and waist to hip ratio.
A similar trend was found for trunk length and levels of GGT and ALP, but the association with GGT was not significant. Conversely, women with longer trunk lengths had higher levels of the enzyme ALT.
There was no association between either leg or trunk length and the levels of the AST enzyme.
What interpretations did the researchers draw from these results?
The researchers concluded that the “childhood exposures (such as good nutrition) that influence growth patterns also influence liver development and therefore levels of liver enzymes in adulthood and/or the propensity for liver damage”.
What does the NHS Knowledge Service make of this study?
There are a number of things to bear in mind when interpreting this study:
- The main issue with this study is that the association between leg length and liver enzymes could be attributable to a number of other factors. Although the authors did try to take into account other factors, such as alcohol consumption, they acknowledge that these adjustments may not have eliminated all confounding.
- The authors used leg length as an indirect measure of childhood nutrition, but it is not clear how good a measure it is, as it probably reflects a number of other factors including genetic inheritance. A specific investigation into the effect of childhood nutrition on liver damage would ideally perform a prospective assessment of childhood nutrition and other childhood exposures and follow these children to adulthood to see if they developed signs of liver damage.
- Although raised levels of liver enzymes were used as an indirect measure of liver damage, it was not clear whether the increased levels that were associated with shorter legs were sufficiently raised to cause the women to have health problems. The authors themselves acknowledge that the differences between groups of women with different leg lengths were small. As only one measurement of liver enzymes was taken, the women’s measurements are not necessarily indicative of their typical levels, as levels of liver enzymes can be affected by medication and by recent alcohol consumption.
- Alcohol consumption, a major factor affecting the liver, was reported by the women themselves, and may have been under estimated because of the social stigma associated with excess alcohol consumption. This could have affected the ability of the authors to accurately take this into account.
- As this sample was in women only, and because it is likely to have mostly consisted of white women, these results may not apply to men or to people from different ethnic backgrounds.
These limitations mean that it is not possible to say for certain that childhood diets (as reflected by leg length) have any effect on liver function as an adult.
Sir Muir Gray adds...
It’s difficult to see what a citizen or even a public health professional could do with this information . We already know that good nutrition in childhood is a good start to life.