Holford Watch: Patrick Holford, nutritionism and bad science

CLARIFICATION: following an e-mail from Patrick Holford , we are pleased to note that he does not advise eating fish three times per day; it appears that this was an error in the newspaper article (now corrected in the online version).

The Independent appears to have responded to Private Eye’s criticism of their describing Holford as “one of the world’s leading authorities on new approaches to health and nutrition” by, um, giving Holford the opportunity to share his wisdom on Seasonal Affective Disorder (SAD). I’ve got a number of problems with this article. What jumped out at me first, though, was that - while Holford is normally willing (too willing, in my opinion) to warn about the dangers of mercury - in the Independent he advises that those concerned about SAD “eat tuna, mackerel, herring or salmon three times a week”. Because some tuna is relatively highly contaminated with mercury, someone who ate it thrice-weekly could well be above the FDA’s recommended maximum mercury consumption.

FDA recommendations for safe dietary mercury levels suggest that adults don’t eat more than 14oz/week of fish with an average of 0.5 ppm mercury (which includes some types of tuna). Children, and women who are or may become pregnant, are recommended to eat significantly lower levels of mercury. Now, these recommendations are precautionary - they have been criticised as over-cautious, and I sometimes eat more than this myself - but Holford could at least be consistent.

It is odd that Holford is apparently disturbed by the low levels of ethylmercury in vaccines - stating that “Tiny amounts of mercury have been shown to promote abnormal methylation” and recommending that tuna should only be eaten once per month due to its mercury content* - but suggests in the Independent that people consume tuna much more often. This is despite the fact that it can easily be the case that “a tuna sandwich contains…more mercury than a typical vaccine dose“. It’s also worth noting that - if you eat canned tuna - this won’t contain the omega 3 fats that are in the fresh stuff.

I’m not convinced that the mercury in fish is - with any kind of ‘normal’ diet - a particular cause for concern, especially for adults who aren’t pregnant. Mercury is toxic, but any effects will be dose-dependent and there are only very low amounts of methylmercury in commercially available fish (and even tinier amounts of ethylmercury in some vaccines). However, if one is going to worry about taking on tiny amounts of mercury, the consequences of limiting consumption of higher-mercury fish (eating less of tasty foods like tuna) are much less severe than the potential consequences of avoiding vaccination. Health ‘experts’ - like Prof Patrick Holford of Teesside University - should keep this type of risk/reward analysis in mind when they make their recommendations.

* Patrick Holford, New Optimum Nutrition for the Mind (2007: Piatkus, Kent), pp. 100-101.