Diet and arthritis

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A question that is very commonly asked is whether diet may have a particular effect on arthritis. The answer is maybe - but unfortunately probably not a lot! Whereupon you will immediately want to inform me that the cider in vinegar or olive oil capsule you take regularly work wonderfully for you. And I would not take issue with you for one moment as every individual is different and medical services does not have all the answer by any means. However I would add that most of the dietary remedies that you may have been recommended by reading the press or by listening to a well meaning colleague have not stood up to tests in properly controlled trials. Also remember that there are often commercial reasons behind promoting products in chronic conditions in which the efficacy of such products may be difficult to assess, and indeed no different from ‘placebo’. It may be worth for a moment explaining what we mean by ‘placebo’.

A placebo effect is that effect that may be gained from simply intervening in treatment of a condition, regardless of whether that intervention works or not. A common placebo effect is seen in drug trials where a dummy tablet is given rather than an active tablet to some individuals who are unaware of the difference (in all such trials the individuals will be told that they have a chance of receiving inactive placebos). It is not uncommon for individuals to improve just with the dummy treatment - the so-called placebo effect. The more dramatic the dummy treatment e.g. an injection rather than a tablet - the greater the placebo effect. Doctors rely on placebo effects all the time – the more they insist or appear confident that a certain treatment will work the more likely such a treatment will work - despite the fact that it may have no effect at all on the underlying disease process. Placebos are by no means a bad thing if the end result is that the patient feels better. Therefore by all means continue to take whatever remedy you believe is helping you feel better - so long as it is not doing your body any harm. Having said all that, there is a little bit of evidence that certain dietary interventions may offer more than just placebo. Certain fish oils taken in large quantities may have an anti-inflammatory effect - even if you do run the risk of smelling like a sardine! One estimate has is that at least six fish meals per week are required in order to gain a potentially useful anti-inflammatory effect. Fish oils contain a large proportion of certain polyunsaturated fats which are the building blocks of molecules called prostanoids (eg prostaglandin). Evening primrose oil contains high quantities of another polyunsaturated fat called gammalinoleic acid or, GLA. The prostanoids derived from marine oil and evening primrose oil may help block certain pathways leading to inflammation. However one does need to take large quantities of these particular substances, and even then the effect may be no more than mild.

Several studies in rheumatoid arthritis have shown some benefits of diet containing fish oils or GLA, such as a reduced need for non-steroidal anti-inflammatory drugs. Of more relevance to us, it has been shown that skin psoriasis improved in some patients taking large quantities of fish oils compared to a placebo. To date there has not been a study which has shown a beneficial effect of fish oil or GLA on the joints in psoriatic arthritis, but more studies are obviously needed in this area.

Similarly although there have been reports that a gluten-free diet can be helpful for psoriasis in some cases, most evidence suggests that there is not a strong link between psoriasis and coeliac disease. In a well conducted US study there was no evidence that the immune markers associated with coeliac disease (anti-gliadin antibodies) were any higher in patients with psoriasis or psoriatic arthritis than healthy controls. Overall, it would be advisable to take anything you are told about diet with an appropriate degree of skepticism – if not a pinch of salt (bad for your blood pressure)!

Professor Neil McHugh
Consultant Rheumatologist
Royal National Hospital for Rheumatic Diseases

This revised and updated version © PAPAA 2008