I agree with Barbara Ehrenreich that it is important to assess carefully the effect of self-help methods on disease prevention, and on improving length of life once diagnosed (Illness is all in the body, July 21). However, her conclusion that any approach involving self-help work amounts to "blaming the disease on sin or some grave moral failing" is unhelpful, and removes the possibility of any impact from the many ways in which people with serious illness empower themselves.

She draws on some recent research while ignoring other important findings. For example, the outcome of a recent study on diet and breast cancer is described as signalling the demise of "theories of disease that blame the sufferer"; yet she doesn't mention recent studies demonstrating the protective effect of exercise in reducing the risk of recurrence in breast and colon cancer (Holmes et al, 2005; Meyerhardt et al, 2006).

Many people with cancer want to have a chance of influencing the outcome of their illness. At the Cancer Resource Centre we daily see people adopting strategies that at the very least are energising, and often result in significant improvements in quality of life. Ehrenreich looks down on "positive psychology", which she sees as promoting the idea that almost any health setback can be conquered with optimism.

It is certainly true that positive thinking can be used in a crass way that amounts to denial. However, when adopted in a way that does not suppress the powerful negative feelings accompanying illnesses like cancer, approaches such as visualisation of medical treatments eliminating tumours can have a significant effect. It vastly enhanced my own ability to stay on top of things when diagnosed with cancer at 31.

Encouraging forms of self-help as an adjunct to medical treatment is not synonymous with "blaming ... people for their diseases". Ehrenreich's article is partly based on a study that examined the impact of psychotherapy on survival, and concluded that there is insufficient evidence of impact to justify further research. However, understanding all the varied impacts of therapy and self-help calls for a different kind of research. An example is the research that was carried out over a 20-year period at the Ontario Cancer Institute. It deployed in-depth interviews with individuals who had taken part in a programme of psychological and spiritual self-help. The research demonstrated a wide range of benefits, such as reduced anxiety and depression, relief of fatigue, and a reported sense that participants' lives had changed for the better. In addition, a small study of 22 patients with incurable cancers showed a strong correlation between the intensity of involvement with the self-help work, and the extent to which people's lifespan exceeded the medical prognosis.

While some people with cancer do prefer to regard the illness as something that can only be affected by medical treatment, many now choose to play an active role. The "narrow-eyed, deeply sceptical attitude" Ehrenreich recommends may be useful for the assessment of evidence, but if life is to be fulfilling after a cancer diagnosis, constructive, creative responses to illness make an essential difference.

· Petra Griffiths is director of the Cancer Resource Centre in London

petragriffiths@cancer-resource-centre.org.uk