Friday January 25 2008
The questionnaire asked about chocolate consumption
“Eating chocolate could lead to weaker bones,” reported the Daily Express today. The Daily Telegraph also covered a new study that has shown that women who ate chocolate every day had less dense bones than those who ate it less than once a week. The Daily Mail quotes the lead researcher as saying, “These findings could have important implications for prevention of osteoporotic fracture.”
The research behind this claim is a cross-sectional study, which by virtue of its design, cannot prove that chocolate consumption causes low bone density in women. Other diet, lifestyle, or environmental factors could have caused the decreased bone density. This finding was also only in women over 70 and so cannot apply to younger women or men. Studies with more robust designs would be needed to confirm this association.
Where did the story come from?
Dr Jonathan Hodgson and colleagues from the Royal Perth Hospital Unit carried out the research. The study was supported by a research grant from Healthway Health Promotion Foundation of Western Australia and from the National Health and Medical Research Council of Australia. The study was published in the peer-reviewed: American Journal of Clinical Nutrition.
What kind of scientific study was this?
The study was a cross-sectional study of Australian women aged over 70 who had participated in a five-year randomised controlled trial of calcium supplementation to prevent osteoporotic fractures. For this latest publication, the authors looked at the data available on women’s chocolate consumption and bone density measurements at the end of the original study (i.e. at five years).
Although 1,460 women were included in the original study, only 1,001 were included in this cross-sectional study. This was primarily because the researchers excluded women who were not able to walk. The women’s chocolate intake and overall diet (including beverages) was assessed through a questionnaire. Bone density and strength measurements were made using three different imaging techniques (ultrasound, computed tomography, X-ray absorptiometry) at three different body sites (the heel, the shin and the hip).
The researchers then used statistical methods to explore whether there was a link between total chocolate intake (including solid chocolate and “chocolate containing beverages”) and bone density and strength. In their analysis, they took into account other factors that may affect this relationship, including age, BMI, smoking status, physical activity, and other dietary factors.
What were the results of the study?
Increased chocolate consumption was associated with lower mean bone density at all the measured sites. When the researchers took into account other factors, such as age, BMI and lifestyle, that could potentially affect this relationship, they found that some of these relationships (e.g. when bone density and strength were measured in the shin) were no longer significant.
What interpretations did the researchers draw from these results?
The researchers conclude that this is the first study to investigate the relationship between chocolate intake and bone structural measurements. They say that although further studies are needed to confirm the findings, their study raises concerns that frequent chocolate consumption may increase the risk of osteoporosis and bone fracture.
What does the NHS Knowledge Service make of this study?
This study has weaknesses that are due to the nature of the study design. The authors themselves recognise the limitations of the study, and say that “additional cross-sectional and longitudinal studies are needed to confirm these observations”.
- Although the study took into account the effects of some factors that could influence the association, there are likely to be others that were not considered. On this point, the researchers say that it is possible that chocolate is a surrogate for some other factor (diet, lifestyle, or environmental) which was not considered or was measured inadequately and therefore chocolate may not be responsible for the observed relation.
- The researchers excluded about 200 women who were not able to walk. This would have introduced a bias if those women had different patterns of chocolate intake and bone density than those who were included.
- The consumption of solid chocolate and “chocolate containing beverages” was combined in their measure of chocolate intake. The study then was not only about “eating” chocolate as the papers have imply.
- The researchers analysed chocolate consumption at one time point (at five years). Although the researchers assessed the persistence of chocolate intake (by comparing intake at year one and year five), they did not use this figure in their analyses. They also did not assess this for “chocolate containing beverages”.
- The study was in women aged over 70 and the findings will not apply to younger women (premenopausal or not) or to men.
Until prospective studies confirm a harmful link between chocolate consumption and bone health, women should not be unduly concerned by the results of this study. Because of its high fat and sugar content, chocolate should be consumed in sensible amounts.
Sir Muir Gray says...
I don’t like chocolate, but if I did I would wait for a systematic review of a number of studies before giving it up. Alternatively, you could carry on with the choc, assume there is a relationship and take more exercise.