Probiotics may boost NK cell activity in seniors, but more evidence is needed

There appears to be a significant benefit of probiotics in natural kill (NK) cell function in elderly adults, reports a new meta-analysis. However, the overall body of evidence does not seem to be convincing, given the low number of studies coupled with high heterogeneity.

Six eligible trials were ultimately retrieved from five electronic databases. Lactobacillus-based probiotics were predominant, used alone in three studies and with a Bifidobacterium add-on in two; in the final study, Bacillus coagulans was the probiotic of choice.

All studies assessed for NK cell activity, though one had processed their assay findings, and was thus ineligible for pooled quantitative analysis. Interferon-gamma was also a common endpoint, evaluated in three trials, but the methods used differed.

Other cytokine endpoints, such as the granulocyte macrophagocyte colony stimulating factor and macrophage inflammatory proteins, were assessed in single studies and were impossible to conduct a meta-analysis for.

Pooled analysis showed that NK cell activity was significantly enhanced among elderly adults who received probiotics (standardized mean difference, 0.777, 95 percent confidence interval, 0.187–1.366; p=0.01). Heterogeneity of evidence, however, was significant (p<0.001).

In addition, the researchers detected considerable methodological weaknesses. In four studies, for example, there had been no mention of any randomization method, while three studies failed to blind participants to either the intervention or placebo.

“More randomized controlled trials with sufficient sample sizes and long-term follow-up are needed to focus on optimal probiotic dose, species, and duration of supplementation for healthy elderly individuals,” the researchers said.