The purpose of this study was to determine the effect of regular ingestion of capsaicin-containing food that is easily available in everyday life on the latency of the swallowing response (LSR). Pickled Napa cabbage was selected as the food for the present study. One portion (10 g) of pickled Napa cabbage provides 1.5 µg of capsaicin. Participants ingested pickled Napa cabbage (10 g) before every meal for 20 days (days 1–20). LSR was measured pre-intervention (day 0) and post-intervention (day 21). The participants then followed their regular diet, without foods containing red pepper, from day 21 to day 27, and LSR was measured on day 28 (follow-up LSR). Sixteen elderly participants (two male, 14 female; age 81.6 ± 9.39 years) and 10 young participants (all female; age 21.6 ± 0.52 years) participated in the study. The pre-intervention LSR was 2.04 ± 1.60 s in elderly participants and 1.27 ± 0.27 s in young participants. In the elderly group, the post-intervention LSR (day 21) was 1.47 ± 1.05  the follow-up LSR (day 28) was 1.99 ± 1.80 s (p = 0.044 and 0.502, respectively, compared to pre-intervention). In the young group, the post-intervention and follow-up LSR values were 1.07 ± 0.20 s and 1.04 ± 0.10 s, respectively (p = 0.016 and 0.038, respectively, compared to pre-intervention). Swallowing function was improved by pickled Napa cabbage containing capsaicin, but capsaicin supplementation may need to be maintained to have an ongoing effect.

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A test statistic is developed for making inference about a block-diagonal structure of the covariance matrix when the dimensionality p exceeds n, where n = N−1 and N denotes the sample size. The suggested procedure extends the complete independence results. Because the classical hypothesis testing methods based on the likelihood ratio degenerate when p > n, the main idea is to turn instead to a distance function between the null and alternative hypotheses. The test statistic is then constructed using a consistent estimator of this function, where consistency is considered in an asymptotic framework that allows p to grow together with n. The suggested statistic is also shown to have an asymptotic normality under the null hypothesis. Some auxiliary results on the moments of products of multivariate normal random vectors and higher-order moments of the Wishart matrices, which are important for our evaluation of the test statistic, are derived. We perform empirical power analysis for a number of alternative covariance structures.

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