In those who had consumed the yogurt, nearly seven in 10 reported no incidence of URTIs during the 12-week period.
Whereas in those who did not consume the yogurt, only three in 10 said they did not experience URTIs.
The findings, published in Pharmaceutical Biology, also found that the duration and severity of URTIs were reduced in individuals who have consumed the yogurt.
A total of 123 subjects completed the trial where they randomised to consume either 250g of Qingrun – a yogurt produced by Bright Dairy – or control yogurt once daily for 12 weeks.
Qingrun was fermented from raw milk and favoured with an appropriate amount of white sugar, loquat jam, snow pear jam, whey protein powder, and food flavours.
Lactic acid bacteria, including Bifidobacterium animalis subsp. lactis Bl-04, Lactobacillus casei, Lactobacillus bulgaricus, and Streptococcus thermophilus, were also added into the Qingrun yogurt.
Of which, the amount of Bifidobacterium animalis subsp. lactis Bl-04 was more than 2bn CFU/100 g.
A previous study by West et al showed that the intake of Bifidobacterium animalis subsp. lactis Bl-04 with 2bn CFU per day was useful in reducing the risk of URTIs in healthy physically active adults.
On the other hand, the control yogurt was processed similarly but without the addition of Bifidobacterium animalis subsp. lactis Bl-04, loquat jam, and snow pear jam.
In addition, a pre-requisite for recruitment is that the subjects have been suffering from common cold four to six times in the past year and live in a haze-covered area in Beijing. Both smokers and non-smokers were recruited.
During the study, the incidence, duration and severity of URTI experienced by the subjects were recorded and evaluated by the Wisconsin Upper Respiratory Symptom Survey–24.
Blood and faecal samples were also collected at the baseline and post-intervention, to determine the changes of immune biomarkers.
The trial showed that the frequency, duration, and severity of URTIs were significantly lower in the group which took the Qingrun yogurt.
For instance, only 27.4 per cent from the Qingrun yogurt group reported experiencing one episode of URTI, while the rate was higher in the control group at 57.4 per cent.
On the other hand, while 4.8 per cent from the Qingrun yogurt group reported two URTI episodes, the control group had 9.8 per cent who experienced two URTI episodes.
The duration of URTI symptoms was also longer in the control group, at 6.16 ± 5.46 days and shorter at 1.95 ± 3.39 days in the other group.
The control group also reported a higher severity score of the URTI symptoms at 14.90 ± 12.25, while the score for the other group was 5.79 ± 9.03.
The frequency of URTI in smokers was also higher than that of the non-smokers.
For instance, amongst the smokers, 25 per cent in the control group and 9.1 per cent in the intervention group reported two episodes of URTI.
For non-smokers, this was much lower at 2.4 per cent from the control group and 2.5 per cent from the intervention group.
The amount of interferon-γ had significantly increased in the Qingrun group as compared with those in the control group.
Interferon-γ is a cytokine that stimulates natural killer cells and is critical to both innate and adaptive immunity.
By the end of the study, the level of interferon-γ increased from 114.49 ± 56.23 pg/ml to 139.49 ± 59.49 pg/ml in the Qingrun group.
It stayed relatively the same at 112.33 ± 59.95 pg/ml to 113.45 ± 65.12 pg/ml in the control group.
The researchers concluded that the Qingrun yogurt showed a protective effect against URTI in adults.
This means that consuming yogurt with probiotics could be a promising dietary supplement for mitigating URTI.
However, it was unknown whether the protective effect of the yogurt was more prominent in smokers than in non-smokers.
“Our results highlighted the superior protective effect of this yogurt against URTI symptoms compared to the control yogurt without Bifidobacterium animalis subsp. lactis Bl-04.
“Loquat leaf and snow pear have been used to treat URTIs in traditional Chinese medicine for centuries. It was reported that flavonoids and triterpene acids isolated from loquat leaves inhibited oxidative stress and inflammation in mice with cigarette smoking-induced chronic obstructive pulmonary disease (COPD).
“Our study is the first to demonstrate the protective effects of a yogurt product containing these two botanical ingredients with probiotic bacterium against URTI, but whether a synergistic mechanism exists remains unknown,” the researchers concluded.
Source: Pharmaceutical Biology
Effect of fermented milk on upper respiratory tract infection in adults who lived in the haze area of Northern China: a randomized clinical trial
Authors: Hong Zhang et al