Bipolar disorder is a chronic disorder that affects the mood, and occurs in over 2% of the general population. It is associated with a substantial reduction in life expectancy, between 10 and 20 years shorter than in the general population. The main cause of this reduction is the presence of other diseases, in particular cardiovascular diseases, dementia or cancer.
As for the pharmacological treatment for bipolar disorder, lithium is one of the main effective medications. Moreover, treatment with lithium has been associated with a protective effect against other diseases, including cognitive impairment and dementia, fractures caused by osteoporosis, stroke, as well as against suicide. However, the effect of lithium treatment on the risk of cancer, especially urinary tract cancer, continues to be controversial.
In a study, the Depressive and Bipolar Disorders Unit, headed by Dr. Vieta, examined the risk of patients with bipolar disorder developing cancer, as well as the role played by treatment with lithium in this interaction. The study carried out, a systematic review, includes data from over 4.5 million people, 59,000 of them with bipolar disorder and 4,500 individuals treated with lithium.
The study reveals that people with bipolar disorder have an increased risk of developing cancer, approximately 20% higher than in the general population. This risk is particularly high (around 30%) if we consider breast cancer in women with bipolar disorder.
The reasons that contribute to the higher prevalence of cancer in patients with bipolar disorder are varied and complex. They include difficulties in accessing primary health care services for prevention and treatment, and social isolation. Moreover, some patients with bipolar disorder have unhealthy lifestyles, with a higher consumption of substances such as tobacco and alcohol, a sedentary lifestyle or poor diets, among other things. Likewise, there are common physiopathological interactions between bipolar disorder and cancer, including hormonal, immune and inflammatory changes, which lead to "accelerated ageing" as well as a genetic and epigenetic predisposition in the two diseases.
Moreover, the study reveals that treatment with lithium does not increase the risk of developing any type of cancer, including urinary tract cancer. What is more, the results of the study point to lithium treatment having a possible protective effect of around 5% against the risk of developing cancer.
The protective effect of lithium treatment against cancer is due to the effects of this molecule on the body's cells. For example, lithium modulates oxidative stress, inflammation, mitochondrial dysfunction and cellular homeostasis, processes closely linked to ageing and stress, which can favour the appearance of cancer cells. Likewise, lithium inhibits the enzyme GSK-3, involved in many cell functions, such as DNA translation, which regulate cell organization and survival.
This study shows that there is a considerable increase in the risk of cancer in patients with bipolar disorder. This highlights the need to implement programmes to prevent the cancer risk factors in patients with bipolar disorder (primary prevention), as well as early detection programmes for cancer in this population, especially breast cancer screening in women with bipolar disorder (secondary prevention). Similarly, the study reinforces the role of lithium as the main treatment for bipolar disorder. The potential protective role against the risk of cancer is yet another beneficial effect of this medication.
Authors: Dr. Gerard Anmella and Dr. Eduard Vieta, Depressive and Bipolar Disorders Unit, Psychiatry and Psychology Service, Hospital Clínic de Barcelona.