The research, published in the journal Nutrients, also suggests that public health officials should issue a clear set of nutritional recommendations to complement messages about the role of hand washing and vaccinations in preventing the spread of infections.
"Around the world, acute respiratory tract infections kill more than 2.5 million people every year," said Adrian Gombart, a professor at Oregon State University (OSU) in the US.
"Meanwhile, there is a wealth of data that shows the role that good nutrition plays in supporting the immune system. As a society we need to be doing a better job of getting that message across along with the other important, more common messages," Gombart said.
Specific vitamins, minerals and fatty acids have key jobs to play in helping the immune system, he said.
Vitamin C, vitamin D, zinc, and an omega-3 fatty acid found in fish, docosahexaenoic acid (DHA), are particularly critical for immune function, according to the researchers, including those from University of Southampton in the UK, the University of Otago, New Zealand, and University Medical Center in the Netherlands.
"The roles that vitamins C and D play in immunity are particularly well known," said Gombart.
He explained that vitamin C has roles in several aspects of immunity, including the growth and function of immune cells and antibody production, while vitamin D receptors on immune cells also affect their function.
"This means that vitamin D profoundly influences your response to infections. The problem is that people simply aren't eating enough of these nutrients," Gombart said.
"This could destroy your resistance to infections. Consequently, we will see an increase in disease and all of the extra burdens that go along with that increase," he said.
The noted that not only a daily multivitamin, but doses of 200 milligrammes (mg) or more of vitamin C -- higher than the suggested guidelines of 90mg for men and 75mg for women in the US -- and 2,000 international units of vitamin D, rather than the 400 to 800 recommended depending on age.
"A number of standard public health practices have been developed to help limit the spread and impact of respiratory viruses: regular hand washing, avoiding those showing symptoms of infection, and covering coughs," Gombart said.
"And for certain viruses like influenza, there are annual vaccination campaigns," Gombart noted.
There is no doubt that vaccines, when available, can be effective, but they are not foolproof, he said.
Gombart emphasised that current public health practices -- stressing social distancing, hygiene and vaccinations -- are important and effective but in need of complementary strategies.
The researchers noted that a nutritional focus on the immune system could help minimise the impact of many kinds of infections.
"The present situation with COVID-19 and the number of people dying from other respiratory infections make it clear that we are not doing enough," he said.
"We strongly encourage public health officials to include nutritional strategies in their arsenal," Gombart added. SARSAR