Fish oil

Sunday 6 June 2010

A team of researchers led by Dr Robert McNamara at the University of Cincinnati, USA, has recently reported in the American Journal of Clinical Nutrition that boys aged 8-10 who take daily dosages of docosahexaenoic acid showed a big improvement in their ability to concentrate and in their performance doing tasks that involved attention.

This report can be used to support the teaching of B.3 Lipids in Option B. It is also interesting to look critically at the findings and the validity of claims involving food supplements.

The structure of docosahexaenoic acid

Docosahexaenoic acid, known as DHA, is an essential fatty acid that is found in fish oil. It has the molecular formula C22H32Oand the IUPAC name docosa–4,7,10,13,16,19–-hexa–enoic acid with all the double bonds in the cis- form. The IUPAC numbering systems takes the carboxylic acid carbon as the first carbon atom. It is also common practice in Food Chemistry to count the carbon atoms from the other end of the hydrocarbon chain. Using this system the first double bond appears on the third carbon atom so it is known as an omega–3 fatty acid.

Evaluating the findings

DHA is widely promoted as a food additive (see advert on left). For example, the US National Library of Medicine, National Institutes of Health states states that DHA is good for people with a history of heart disease and also for promoting healthy brain development in children along with other claims (such as a lack of DHA in the brain being associated with the onset of Alzheimer’s disease).

Clearly there are strong commercial considerations when research into food supplements supports or contradicts such claims. If the reference above is scrutinized carefully it will be see that its two authors. L.A. Horrocks and Y.K. Yeo, work for Docosa Foods Ltd, 1275 Kinnear Road, Columbus, OH 43212-1155, USA. This does not mean that their claims are wrong but clearly they are likely to be putting the benefits of such a food supplement in the best possible light. If you look at the Wikipedia reference for docosahexaenoic acid it currently states that a citation is needed to support the claim that DHA supports healthy brain development in young children. This underlines the importance to the industry of the findings reported recently by McNamara et al.  

McNamara and his team are obviously very much involved in research into the benefits of docosahexaenoic acid as they are currently carrying out a separate trial into its effect on children suffering from clinical depression. They are also looking at how effective it is to tackle attention deficit hyperactivity disorder (ADHD) in children. These trials are ongoing and the results have not yet been evaluated and published.  Both the abstract (at no cost) and the full paper (for a small fee) that has been recently published by McNamara et al. on improvements in the concentration of young boys are available online. We teach students to evaluate their own work critically and for the need to repeat their experiments several times to ensure that the results are reproducible in order to give them validity. When dealing with purely chemical systems this usually presents few problems as the work can be reproduced by others using exactly the same conditions as there are relatively few variables to control. If different results are found then usually one of the variables has not been controlled properly1. The effect of food supplements on the human body is a very different scenario as no two humans are identical so there is much less control of the variables. McNamara’s conclusions on the effect of DHA on boys aged 8-10 are based on only 33 volunteers.  Some of these were randomly given a placebo which reduces the number actually given the DHA.  Those who received a low dose showed less change than those given a higher dose.  The effect on the activation of the dorsolateral prefrontal cortex was determined using functional MRI. The question to be asked is how valid is such a small sample? This result will prove important to the food supplement industry. Statistically the sample is significant but should the sale of food supplements depend on such a small sample or should much larger trials be carried out before such significant claims can be made? 

1. A good example of this is the addition of hydrogen bromide to asymmetric alkenes. In the early literature some researchers found the expected Markovnikov addition product, but others found anti-Markovnikov addition occurring. It was later realized that the alkene needed to be carefully distilled to remove the presence of peroxides in order to get only Markovnikov addition so that the only mechanism operating was electrophilic addition. In the presence of peroxides the faster free radical mechanism predominated.


Tags: Food supplements, DHA, functional MRI, EPA