Nutrition has a key role in cutting the risk of several infections, although exactly how it boosts immunity is complex and not fully understood.
Vitamins A, E, C, and D have already been deemed to aid the normal functioning of the immune system in the European Union, and the American Nutrition Association suggests these vitamins may also help stave off respiratory infections.
In a recent study at Imperial College London, researchers found that high vitamin A, E, and D intake may be linked to fewer respiratory complaints in adults.
The study is published in BMJ Nutrition Prevention & Health. One author is Shane McAuliffe.
In the study, the team wanted to know whether the intake of these vitamins from both diet and supplements might be linked to respiratory complaints in a national sample of UK adults.
They used data from 6115 adult participants in the 2008-2016 National Diet and Nutrition Survey Rolling Programme (NDNS RP).
Respiratory complaints were reported by the participants and had not been diagnosed by a clinician.
They were broadly defined and included both infectious and non-infectious conditions, such as colds, chronic obstructive pulmonary disease, and asthma.
The researchers looked at dietary intake only (continuous exposure) and that from diet and supplements (binary exposure).
They found the respondents with respiratory complaints were generally older and less likely to say they regularly took vitamins A, E, C or D supplements.
Vitamin A and E intake from both diet and supplements were linked to a lower prevalence of respiratory complaints.
Major dietary sources of vitamin A include liver, whole milk, and cheese, as well as carrots, dark green leafy vegetables, and orange-colored fruits.
Major dietary sources of vitamin E include vegetable oils, nuts, and seeds.
And vitamin D intake from supplements, but not from the diet, was linked to fewer respiratory complaints, suggesting that the findings add to the current scientific debate on the value of vitamin D supplementation.
These findings are in line with the view that supplementation is critical to ensuring adequate vitamin D status is maintained and potentially indicate that intake of vitamin D from diet alone cannot help maintain adequate vitamin D status.
The team says it seems sensible to provide supplementation of this key vitamin, particularly to people most likely to be deficient.
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