People who get enough vitamin A, D and E may be less likely to complain of coughs and sore throat, though it's not clear the nutrients are the reason why, new research suggests.
The study, of over 6,100 U.K. adults, found that those who consumed more of the vitamins were less likely to have "respiratory complaints" -- like coughs, "chest" infections, trouble breathing and sore throat.
Vitamin A and E from food or supplements were tied to a lower likelihood of respiratory woes, as was vitamin D from supplements.
None of that, however, proves that vitamins ward off respiratory ills -- including the one on everyone's mind, COVID-19.
For one, only 33 people in the study lodged respiratory complaints, with the sources of those symptoms -- whether infections or chronic lung conditions -- being unclear.
And, in general, surveys like this can only point to correlations, not cause-and-effect relationships.
"We cannot confirm that this relationship is causal," said lead researcher Suzana Almoosawi, of Imperial College London's School of Public Health.
There could be many things that separate people with high or low vitamin intake. The researchers were able to account for some -- like household income, smoking and overall calorie consumption -- but not all.
"These findings are interesting, but definitely not conclusive," said Dr. Daniel Jobe, of Novant Health Primary Care Lindley Park, in Greensboro, N.C.
"It's important to remember that even if two things occur together, they may not actually be related," said Jobe, who was not involved in the study. "It may be a coincidence, and one thing may not be the cause of another."
Along with that issue, Jobe said it's difficult to draw any conclusion based on such a small number of people reporting on "broad and nonspecific" symptoms.
"It's hard to know what the higher vitamin intake may really be improving," he said.
Almoosawi said her team hopes to do an additional study in a group of people they follow over time, to better establish whether vitamin intake is linked to lower risks of future respiratory symptoms.
The findings, published online Oct. 27 in the journal BMJ Nutrition, Prevention & Health, come from a larger survey that, every year, collects health and diet information from a random sample of British households.
Of 6,115 adults surveyed over eight years, 33 reported various respiratory symptoms. Overall, their average intake of vitamins A and E from food was somewhat lower, versus people with no respiratory complaints.
Food sources of vitamin A include red and orange vegetables, dairy products and fortified cereals; vitamin E is found in vegetable oils, nuts and seeds, and leafy green vegetables.
When the researchers accounted for the other factors they could, people with higher vitamin A and E intake -- from food or pills -- were less likely to report respiratory symptoms. The same was true of people who took vitamin D supplements, versus those who didn't.
Vitamin D has been a hot health topic in recent years, and that has ramped up with some studies hinting that vitamin D deficiency could make people more vulnerable to severe COVID-19 infection.
Research has found, for example, that patients with sufficient vitamin D levels in their blood are less likely to have severe COVID-19 complications than those with low levels. Again, though, those findings do not prove cause and effect.
For now, Almoosawi said, "it seems sensible" for people to take vitamin D, since it is present in few foods and deficiency in the vitamin is common. The body synthesizes vitamin D when the skin is exposed to sunlight, which means that people with little sun exposure and those with dark skin are among the groups at risk of vitamin D deficiency.
Experts recommend that most children and adults get 600 IU of vitamin D a day, while adults older than 70 need 800 IU.
Jobe agreed it's hard to get enough vitamin D from food alone. So, he suggested people have their blood levels of vitamin D measured, and then take a supplement if needed. Other than that, he said a healthy diet that includes fruits, vegetables, plant oils and nuts should ensure an adequate supply of vitamins A and E.
But, Jobe said, more research would be needed to show whether those vitamins can help ward off any respiratory ills.
Visit the U.S. National Institutes of Health for more on vitamin D.
SOURCES: Suzana Almoosawi, PhD, BSc, senior teaching fellow, School of Public Health, Imperial College London, U.K.; Daniel Jobe, MD, Novant Health Primary Care Lindley Park, Greensboro, N.C.; BMJ Nutrition, Prevention & Health, Oct. 27, 2020, online