WORK OUT TO BEAT BUGS
Most people know about the benefits of exercise for our heart, waistline, muscles and bones.
Fewer are aware of how it supports our immune defences, especially as we age. Production of naive T cells, which raise the alarm when they detect infections the immune system has not encountered before, declines as we get older.
Research published by Professor Janet Lord's group at the University of Birmingham recently found that cyclists aged 55 to 79 were generating as many of these cells as young adults and had more regulatory B cells, which help to prevent autoimmune diseases.
Other studies show moderate to vigorous exercise reduces the risk of upper respiratory tract infections, including the common cold.
ENSURE ENOUGH SLEEP
Sleep is important to the functioning of the immune system.
Research suggests that white blood cells in those aged 65 and over who sleep six hours or fewer a night may be less effective in dealing with invading pathogens than cells from those who sleep more. Sleep deprivation also makes people more susceptible to colds and flu.
MIX UP YOUR MENU
Our guts contain trillions of microbes that play key roles in the immune system.
For example, they promote the production of T cells, which help to trigger immune responses and prevent autoimmune diseases.
Having a low-fat, high-fibre diet with plenty of vegetables promotes a broad range of gut bugs and boosts levels of beneficial bacteria.
"Having a varied diet is likely to be better for your bacteria which is, in turn, likely to be better for your immune function," says Professor Sheena Cruickshank of the University of Manchester.
BEFRIEND FRIENDLY BACTERIA
Probiotics - live bacteria or yeasts added to yogurts or taken as supplements - can reduce the risk of infectious diarrhoea linked to antibiotic use and help those with ulcerative colitis or pouchitis, a complication of surgery for ulcerative colitis.
However, most of the claims made for probiotics are not supported by good-quality research evidence, despite a global market estimated to be worth about US$40 billion (S$53 billion).
Prebiotics - non-digestible food ingredients that help existing gut probiotics grow - are also available.
There are studies that suggest benefits, but most are small-scale and industry-funded.
"It's a huge business, but at this stage it's not clear which bacteria we might want to nurture to promote health-giving effects, and most people could probably get the same effects with a healthy, balanced diet," says Prof Cruickshank.
MODERATE YOUR DRINKING
Drinking to excess can leave you with more than a hangover.
A 2014 study found that drinking four to five shots of vodka reduced levels of white blood cells, which combat infections and cancer, for up to five hours after peak intoxication.
Heavy drinking has also been found to undermine the ability of immune cells called macrophages to engulf bacteria.
Smokers are more prone to inflammatory diseases and infections such as pneumonia and flu than non-smokers.
Research suggests this may be partly down to nicotine undermining the ability of white blood cells called neutrophils to ingest and kill harmful microbes.
Smokers also have fewer friendly bacteria and more pathogens in the nasopharynx, the upper part of the throat behind the nose, and higher levels of bacteria that cause skin infections and oral diseases .
GET SOME SUNSHINE
Our bodies create vitamin D when our skin is exposed to sunlight outdoors.
Vitamin D helps to keep our finely tuned immune systems in balance by, for example, stimulating the development of cells that prevent the autoimmune responses seen in conditions such as inflammatory bowel disease, multiple sclerosis and rheumatoid arthritis.
It is also used by macrophages to help kill harmful bacteria, and supports our defences against colds and flu.