Thursday November 5 2009
NHS Choices staff face many hardships in the name of science
“Nibbling dark chocolate can seriously improve your health – and even help you look younger,” according to the Daily Mirror. The newspaper says a new study suggests that chemicals in dark chocolate (called flavanols) could help prevent wrinkles and skin cancer caused by sunlight.
There are several major limitations to the way this study was conducted, as well as to the way it was reported by newspapers. As attractive as these claims are, they are unlikely to be true. The assumption that the results of this study can be applied to the ageing of skin or skin cancer is wrong. Some newspapers have correctly pointed out that the dark chocolate studied in this research is not the type that can be bought in shops.
While dark chocolate may be tasty, there must be more rigorous research into the substances it contains if today’s headlines are to be supported by science.
Where did the story come from?
The research was carried out by Dr Stefanie Williams and colleagues from London University of the Arts and European Dermatology London, a private dermatology clinic which provides both medical and cosmetic services. The study was funded by the London University of the Arts and was published in the Journal of Cosmetic Dermatology, the official journal of the International Academy of Cosmetic Dermatology.
The Daily Telegraph interpreted this study as showing that dark chocolate protects against ageing, whereas the Daily Mail has questioned whether it might protect against wrinkles.
What kind of research was this?
This study was designed to be a double-blind, randomised controlled trial which tested whether chocolate consumption had a protective effect against skin damage from light exposure.
The researchers recruited 30 healthy subjects and split them into two groups of 15. Each group was given chocolate that was either high in flavanols (HF) or low in flavanols (LF). Flavanols are a class of flavonoids, which are plant-derived substances that are believed by some to have antioxidant properties. Flavanols are also found in foods such as green tea, pomegranates, goji berries and blueberries. The volunteers were asked to eat 20g of the chocolate every day for three months.
Randomised double-blind studies are the ideal study type for this sort of research, but they need to be conducted and reported correctly. The way that participants are randomly allocated to the two groups (randomisation) and the way that the allocation was kept secret from the study investigators (blinding) need to be described in detail. This was not done in this publication.
What did the research involve?
In this study, the researchers recruited 22 healthy women and eight men with an average age of 43. They selected people who were considered pale and fair skinned according to the Fitzpatrick skin classification scale, an accepted scale used to class people’s complexion and tolerance of sunlight. This means that all patients in this study either burn easily (phototype II) or tan after an initial burn (phototype III). It is important to know how many of each phototype were allocated to the HF and LF groups and also how many in each group were men. This information is not stated in the publication, so it is not possible to tell how successful the researchers’ randomisation process was.
The HF chocolate was manufactured in Belgium using a method that the researchers say preserves the naturally high level of flavanols found in cocoa beans. The LF chocolate was made by a more common method using higher temperatures. It is not clear if the chocolates tasted different. As this was not tested, the participants and researchers may have been aware of which type of chocolate was being eaten.
Researchers tested the skin of all participants at the start of the study and after the 12-week course of chocolate. They used a testing method called minimal UVB erythema dose (MED), in which an automated device delivers increasingly strong doses of ultra-violet light to the front of the forearms.
MED is measured according to the power of the light, the area of the light beam and how long it is applied to the skin, and is expressed as units of J/cm2 (joules per square centimetre). The researchers adjusted the strength of the MED doses for the individual skin types and recorded the level of UV light at which the skin became burned.
What were the basic results?
Of the 30 subjects recruited, 28 completed the study. After the 12 weeks, the average MED in the LF chocolate group did not change, while in the HF group it increased by more than double.
- For the people eating LF chocolate, the MED at the start was 0.124 J/cm2 and increased to 0.132 at week 12 (not statistically significant).
- For the people eating HF chocolate, the MED at the start was 0.109 J/cm2 and increased to 0.223 at week 12 (statistically significant).
How did the researchers interpret the results?
The researchers say that “our controlled, double-blind, randomized in vivo study demonstrated, for the first time to our knowledge, that regular consumption of a chocolate rich in flavanols confers substantial photoprotection and can thus be effective at protecting human skin from harmful UV effects.” They say that conventional chocolate had no such effect, and that the main underlying mechanism of action is likely to be the anti-inflammatory and antioxidant activity of cocoa flavanols.
This small study has several problems that mean care should be taken when interpreting its results. In particular, this study did not look at long-term damage to the skin, ageing of skin or people’s risk of skin cancer, which were all discussed in the press coverage. The actual measure assessed was skin burning in volunteers with an average age of 43.
In the researchers’ reporting of their results, there was a lack of detailed description of the blinding and randomisation procedures used to allocate people to groups. This means it is unclear whether the large difference in the way that skin burned or tanned between the groups was due to differences in the participants’ skin types or chocolate consumption.
Although the administration of UV light to cause the “erythema dose” may have been done objectively, it is not clear how the researchers assessing skin reaction were blinded and whether a sound method was used to prevent them knowing which chocolate group a participant was in.
While the idea that eating chocolate every day can protect the skin is appealing, this research has a number of limitations. It is sensible to reduce the risks of skin ageing and skin cancer by following current sun safety guidelines.