There are many reasons why someone might have lower than usual immunity. Dr Brewer says that “one theory is, as people get older, they develop more vitamin and mineral deficiencies that contribute to reduced immunity with higher levels of inflammation”. She points to a recent study from Oregon State University which found that people aged 55 and over who took a daily multivitamin and mineral supplement for 12 weeks were able to fight off infections twice as fast as those taking a placebo.

But it’s about more than just nutrition. Have you ever noticed that you get wiped out with a cold just before a job interview or big event? That’s because stress has a huge impact on our immunity, says Dr Brewer: “Numerous studies have demonstrated that long term stress has the ability to reduce the functionality of key components of the immune system which can, in turn, leave you open to infection.”

Feeling run down? How to support your immune system when it’s running low