A randomized, double-blind, placebo-controlled clinical trial to evaluate the efficacy and safety of heat-treated Lactobacillus plantarum nF1 for immune function

INTERVENTION: Dietary Supplement : Subjects will be randomly allocated to placebo or experimental group and take 1 capsule per day for 8 weeks CONDITION: Factors influencing health status and contact with health services PRIMARY OUTCOME: NK cell activity (%) et al. SECONDARY OUTCOME: Adverse events et al. INCLUSION CRITERIA: 1) Subject who voluntarily agrees to participate and signs in informed consent form 2) Healthy people, 20 = age < 70 3) Those who have had symptoms of upper respiratory tract infection (including colds) at least twice a year as of 2019, before the outbreak of COVID‐19, and have had symptoms every year before that 4) White blood cell(WBC) ranged “normal”