Background: Age-related changes in the physiology and intestinal function of the elderly render them more susceptible to gut-related illnesses. Probiotic dietary supplementation has been shown to enhance the health indices in the elderly.

Objective: To determine the effect of three different doses [5 x 109 CFU/day (high), 1.0 x 109 CFU/day (medium) and 6.5 x 107 CFU/day (low)] of Bifidobacterium lactis HN019 (DR10TM) on the intestinal flora of elderly human subjects and the dose response effect.

Design: Randomised, double-blind and placebo-controlled human dietary intervention study consisting of four groups of 20 elderly (over 60 years old) volunteers. Each volunteer consumed 250 mL per day of reconstituted skim milk (RSM) which either did not contain any probiotic supplement (placebo group) or contained B. lactis HN019 at different levels (low, medium and high dose groups). The study comprised three stages: a 2-week pre-intervention (without any supplement), followed by 4 weeks of test feeding (dietary intervention) and then a 2-week washout period.

Results: After dietary intervention, statistically significant increases in bifidobacteria, lactobacilli and enterococci were observed. At the end of the 4-week feeding period the mean number of bifidobacteria recorded in the placebo group were 9.31 +/- 0.01 log CFU/g of faeces. In the high, medium and low dose groups the bifidobacteria levels were significantly (p < 0.006) higher (9.88 +/- 0.1, 9.75 +/- 0.14 and 9.74 +/- 0.11 log CFU/g of faeces, respectively), when compared to the respective pre-intervention levels. There were no significant differences (p superior 0.05) between the responses of the different dose groups, indicating that even the lowest dose tested augmented the changes in bifidobacteria. Similar trends were observed for lactobacilli and enterococci. In contrast, the counts of enterobacteria were reduced in all the probiotic dose groups.

Conclusion: The present study showed that dietary supplementation with B. lactis HN019 significantly increased the number of resident bifidobacteria and reduced the enterobacteria counts. In addition, enterococci and lactobacilli were also increased. Based on this study and already published clinical evidence (4, 5, 8, 9) we conclude that, B. lactis HN019 is a suitable probiotic for elderly human subjects and even the lowest dose (6.5 x 107 CFU/day) tested is able to confer desired changes in the intestinal microflora.