A randomised controlled clinical trial funded by Kagome Co, a Japanese manufacturer of tomato-based products and fruit and vegetable juices, tentatively supports the use of lactic acid bacteria (LAB) Levilactobacillus brevis KB290 and vitamin A - particularly for adults under 40.
“The results of this trial suggest that the combination of KB290 and βC might be a possible candidate supplement for protection against the seasonal influenza virus infection in humans aged <40, although further clinical studies are needed to confirm the concrete preventative effect of this combination on influenza,” wrote the researchers in the journal Nutrients.
Vitamin A has been studied for its effects on the immune system as well as its protective effects against flu infection, while LAB have been reported to exert immunomodulatory effects on the respiratory tract and protect against flu infections. However, the combined effects of LAB and vitamin A on flu infection have not been investigated in a human trial.
A previous trial carried out by some of the researchers in this study had already demonstrated that the administration of KB290 or vitamin A suppressed weight loss and viral titer elevations in mice challenged with an influenza type A virus. It also found that the combination of KB290 and vitamin were more effective at suppressing weight loss than when they were administered individually.
“These results made me think that combining them would achieve better protection results than individually,” lead researcher Shohei Satomi, of Kagome Co’s Innovation Division, told Nutraingredients.
As excess intake of vitamin A can lead to toxicity in humans, the clinical trial used the pro-vitamin A β-carotene instead.
“We performed a randomised controlled trial to investigate whether a combination of KB290 and β-carotene could reduce the incidence of influenza and common colds as well as alleviate clinical symptoms in healthy Japanese adults,” wrote the researchers.
The randomised, double-blind, placebo-controlled, parallel-group study ran between 16 December 2019 and 8 March 2020, comparing a KB290 and β-carotene beverage with a placebo. 2148 healthy Japanese adults (1080 in the experimental group and 1068 in the placebo group), completed the trial, drinking one 200ml bottle of ether the KB290 and β-carotene beverage or a placebo beverage daily for 12 weeks. Influenza incidence, fever incidence and fever duration were evaluated as the primary endpoints.
There was no significant difference in the number of influenza cases between the two groups as a whole: the rate of influenza cases was 2.9% in the experimental group and 3.4% in the placebo group. Nor was there any notable difference in fever incidences or fever duration between the two.
Protection for the under 40s?
However, when the results were broken down by age, the researchers noted that in subjects aged under 40, the number of influenza cases in the KB290 and β-carotene group was significantly lower than in the placebo group (1.9% vs 3.9%). By contrast, in the subjects aged 40 and over, the rate of influenza cases was similar in both groups.
“We showed that the consumption of KB290 + βC did not significantly reduce influenza incidence, fever incidence, or incidence/degree of clinical symptoms in the subjects in this trial. However, we provided evidence that the experimental beverage significantly reduced influenza incidence in the subjects aged <40 y, without any associated serious adverse events,” wrote the researchers.
The researchers speculated that the lack of significant differences in the analysis of all subjects may be attributed to a lower than usual flu rate during the 2019-2020 winter season (partly thought to be due to COVID-19).
“This winter season might not have been suitable for the evaluation of the preventative effects of KB290 + βC on influenza due to its low prevalence,” they wrote.
Nevertheless the subgroup analysis on the subjects aged under 40 showed that this combination significantly reduced influenza incidence.
“This could be due to low awareness of prevention against infection and low βC intake from the daily diets of subjects aged <40,” noted the researchers.
Satomi hypothesises that this ingredient combination strengthens the mucosal barrier and the innate immunity in the host.
The researchers acknowledged that further clinical studies were needed to confirm the preventative effect that was observed in the under 40s, and recommended that future studies should investigate the mechanisms at work.
Satomi.S., Waki,N., Arakawa, C., Fujisawa, K., Suzuki, S., Suganuma, H.
"Effects of Heat-Killed Levilactobacillus brevis KB290 in Combination with β-Carotene on Influenza Virus Infection in Healthy Adults: A Randomized Controlled Trial"