Before starting on nights, you are entitled to a free health assessment and regular (e.g. annual) health assessments thereafter. These checks would normally be medical examinations, but may be in the form of a questionnaire.
A common assumption for someone on a nightshift is that their body will adapt to working at night. In fact, it doesn't and never will. Even after 20 years, a nightworker will still be locked on to the same sunlight-dependent body cycle (known as the circadian rhythm) as dayshift workers. Essentially, to carry out their tasks a nightworker has to override his or her desire to sleep.
The health consequences of doing so are severe for an individual. While occasional nightshift working is fine, sustained nightshift working is associated with an elevated risk of cancer, cardiovascular disease, type 2 diabetes and some serious pathologies. Accordingly, no-one should work nights frequently or permanently.
If your health is particularly badly affected by nightwork you should, if it is possible, be offered alternative suitable daywork.