A poll of 2,000 adults found a quarter consume more alcohol and 28 per cent have different sleeping patterns during the warmer months.
Nearly a fifth (20 per cent) skip breakfast, while 19 per cent don’t exercise as much as they usually would.
And 20 per cent forget to take their daily vitamins, supplements or fortified products.
Despite this, 23 per cent are keen to get back into a healthy routine as 38 per cent think their overall health improves when doing so.
While 69 per cent claim they have weak immunity, 22 per cent are keen to boost this but are unsure how to.
Tom Hickton at Actimel, which commissioned the research to launch its Immunity Report, said: “Our research shows that people across the UK want to give their immune systems some support as the seasons change but aren’t sure how to do so.
“Diet is a great place to start – we have seen that the nation isn’t getting their daily intake of vitamins D (30 per cent) and B6 (35 per cent) needed for immune support.”
Swansea is the least likely to have a balanced diet
The study also found Brits are keen to get their healthy lifestyles back on track as a quarter plan to eat healthier (26 per cent), exercise more (25 per cent) and eat or drink products intended to improve immunity (21 per cent).
But breaking bad habits could prove to be difficult as 39 per cent admit to regularly snacking at night and 43 per cent indulge in sweet treats multiple times a week.
Further to this, 19 per cent have processed meals up to six times a week - with those living in the North East (4.4) and Yorkshire (4.5) consuming way above the average weekly amount (3.9).
However, 77 per cent do follow the NHS recommended healthy balanced diet - with those living in Brighton and Hove, Cambridge and Liverpool most likely to do so, and adults in Swansea least likely.
When quizzed on alcohol consumption, 40 per cent of Londoners - who already live among high levels of pollution - have a higher-than-average weekly intake compared to the average adult (9 units) along with those in the South West (10 units).
In comparison, the North West (7.4) and Midlands (8.1) are the regions which drink the least.
Those in the capital are also predicted to have lower levels of immunity than those in the West Midlands, but higher than those in the North West.
Compared to the daily average (three hours), London and Scotland spend more time exercising per week whereas those in East Anglia and the Southwest keep active much less.
Supporting personal immunity
The study also found 57 per cent manage to achieve more than seven hours sleep, which, according to the Actimel Immunity Report, is the target amount - with the remaining reporting they under-sleep.
When it comes to regional splits, those in the South West get the most shut-eye and people in the West Midlands manage the least, according to the OnePoll figures.
Immunologist Dr Jenna Macciochi PHD added: “The research shows how despite most people being aware that the change in seasons can have a negative impact on health, they are confused as to where to start and find it hard to implement lifestyle-based health changes.
“There is also an education gap when it comes to the most effective ways we can help support a well-functioning immune system, as there appeared to be a lack of awareness around ensuring enough daily vitamin D and consuming fortified products, which can be a real help as we move into winter.
“It’s good to remember we can all take small steps to support immunity through exercise, good sleep and diet and small changes can make a big difference.”
