Health and Lifestyle

Our research focuses on identifying modifiable lifestyle risk factors for common and serious diseases. How does lifestyle – smoking, diet, exercise and use of hormonal therapies – influence risk of disease, especially in middle and old age, and what aspects of lifestyle might individuals and society consider most important for disease prevention and public health?

smoking

In the UK, smoking remains the leading preventable cause of death, and is a major cause of cancer and cardiovascular disease. In the Million Women Study, we are investigating the full effects of smoking and of stopping smoking at various ages on a number of health outcomes, in a cohort who were the first generation of women to have smoked heavily from a young age into later middle-age. We have shown that even after a lifetime of smoking, women who stop smoking in middle age can still substantially reduce their risk of dying prematurely from a smoking-related disease (Pirie et al, 2013). We have also shown how smoking affects different types of skin cancer in different ways (Pirie et al, 2018).

Obesity

Obesity continues to be a major factor influencing the burden of disease globally. In the UK and other countries, we investigate the impact of obesity on health and on the healthcare system across a range of major diseases, including cancer, heart disease and fractures.  In the Million Women Study, we found that overweight and obesity have a major impact on rates of hospital admission for a wide range of conditions including joint replacements, heart disease - and some less obvious diseases such as carpal tunnel syndrome (Reeves et al, 2014). This work has also led to the quantification of the burden to the NHS in terms of healthcare costs of excess weight (Kent et al, 2017). Obesity can vary in its effect on cancer risk: we have found that a higher body mass index is associated with an increased risk of oesophageal adenocarcinoma but a lower risk of oesophageal squamous cell carcinoma (Sweetland et al, 2023). Obesity is also closely related to other topics of interest in the Unit, such as diet, physical activity, hormones and childhood growth.

Diet

The EPIC-Oxford cohort was set up to look at diet and lifestyle in relation to cancer and has published many papers on the effect of diet on cancer risk. Now, researchers who work on the EPIC-Oxford cohort look at the impact of diet on several health conditions. Our research has demonstrated lower risks of obesity, ischaemic heart disease, diabetes, stomach cancer and perhaps haematological cancers in vegetarians compared with non-vegetarians, but also higher risks of stroke and fractures. Recruitment into EPIC-Oxford was targeted at vegetarians and other people interested in diet and health, as well as the general population. Participants have been followed-up for nearly 30 years by means of repeat questionnaires and linkage to NHS medical records. In May 2024, work began on a new phase of EPIC-Oxford, where we plan to re-survey all participants in the existing cohort and recruit 80,000 new participants, which will result in the world's most informative resource for studying the impacts of plant-based diets.

We are also looking at diet and cancer risk in the Million Women Study, and have published the single largest study ever conducted on diet in relation to colorectal cancer risk (Papier et al, 2025) as well as a comprehensive investigation of diet in relation to breast cancer risk (Key et al, 2019).

Physical activity

We have used the Million Women Study dataset to consider questions of interest in physical activity epidemiology - such as the different effects of activity on risk of fracture at different sites (Armstrong et al, 2012; Armstrong et al, 2020) and the relationship between physical activity and heart disease risk (Armstrong et al, 2015). We have shown that inactivity is unlikely to be risk factor for dementia (Floud et al, 2020), and we are currently investigating the association between physical activity and cancer risk.

We continue to study the risks and benefits associated with use of hormonal therapies.

The Million Women Study was set up to investigate whether menopausal hormone therapy, commonly known as HRT, was associated with breast cancer risk. In 2003, the Million Women Study showed that women taking HRT were at an increased risk of developing breast cancer, with an estimated 20,000 UK women aged 50–64 having potentially developed the disease due to HRT use (Beral et al, 2003). Analyses in the Million Women Study demonstrated that the effects of HRT vary considerably by pattern of use and tumour subtype (Beral et al, 2011). In 2005 the Million Women Study confirmed that post-menopausal women who have not had a hysterectomy and are taking oestrogen-only HRT, are at an increased risk of endometrial cancer (Beral et al, 2005). The study also showed that the risk of endometrial cancer increases in women who take the HRT drug tibolone, but may be reduced in women taking combined oestrogen-progestogen HRT. Results of the Million Women Study published in 2007 showed that women taking HRT were at a slightly higher risk of ovarian cancer (Beral et al, 2007). The study, analysing 948,576 postmenopausal women over five years, found that for every 1,000 women taking HRT, 2.6 developed ovarian cancer, compared to 2.2 in those not taking HRT.

The study has also provided valuable evidence regarding the association of HRT with many other conditions including venous thromboembolism, gallbladder disease, cataracts, and fracture risk, thus providing a more complete overview of the risks and benefits associated with HRT use (Banks et al, 2004; Sweetland et al, 2012; Liu et al, 2008; Floud et al, 2016).

In 2019, the Million Women Study was a major contributor to a report using data from 58 studies around the world which provided definitive evidence on the long-term effects of taking HRT on the risk of breast cancer. Compared with women who had never taken HRT, women who started taking HRT after menopause had a significantly increased risk of invasive breast cancer. The longer women took HRT, the greater the risk. In women who stopped taking HRT, their risks of breast cancer were lower but remained elevated more than 10 years after stopping (Collaborative Group on Hormonal Factors in Breast Cancer, 2019).

We also research the effects of hormonal contraceptives on breast cancer and other outcomes. As contributors to collaborations, we have shown that the use of hormonal contraceptives results in strong long-term protection against both endometrial and ovarian cancer (Collaborative Group on Epidemiological Studies of Endometrial Cancer, 2015; Collaborative Group on Epidemiological Studies of Ovarian Cancer, 2008). Most recently, we have shown that current or recent use of progestagen-only contraceptives is associated with a slight increase in breast cancer risk (Fitzpatrick et al, 2023). 

environmental and genentic factors

We have a programme of research on social factors, such as marital status and social participation (Floud et al 2015). Our work on lifestyle (environmental) factors gives part of the picture - for many conditions we are also studying genetic influences (eg for prostate cancer and breast cancer), (Travis et al,2010; Reeves et al, 2010)  as well as biochemical factors (Schmidt et al., 2015) which may help to explain how lifestyle and genes affect development of disease.