People who work night shifts may be more at risk of breast or prostate cancer because of hormonal changes.

Night shift work has previously been linked to a raised cancer risk, but it wasn't clear why. Now a study by the Pompeu Fabra University in Barcelona suggests increased levels of sex hormones, such as oestrogen and testosterone, at the 'wrong' time may be to blame.

More than 100 people who worked different shifts gave urine samples across a 24-hour period; their hormone levels were also measured. Night workers were found to have significantly higher levels of sex hormones at the wrong time, such as testosterone peaking between 10am and 2pm, rather than between 6am and 10am.