Contribution to the study of kefir and its by-products on skin health

Supervised by:
  1. Catarina Rosado Ro Director
  2. Patricia Dias Mendoça Rijo Co-director
  3. María Victorina Aguilar Vilas Co-director

Defence university: Universidad de Alcalá

Fecha de defensa: 13 June 2022

  1. Maria do Céu Goncalves da Costa Chair
  2. Ana María Díaz Lanza Secretary
  3. André Rolim Baby Committee member
  1. Ciencias Biomédicas

Type: Thesis


The skin is a functional organ with a fundamental role in the maintenance of body homeostasis. Skin barrier dysfunction correlates with atopic dermatitis (AD) clinical severity and together with immune dysregulation are at the onset of AD. Ingestion of probiotics has shown beneficial effects on skin health, namely in the reduction of severity in AD. Kefir, a traditional fermented food, has numerous health benefits due to its unique microbial and chemical composition, which is reflected in both its microbiological diversity and its excellent nutritional value, thus making its application as a probiotic in the intestine-skin relationship of the utmost interest. However, in the literature there is still no evidence on the impact of a diet containing kefir on skin health, of either healthy or atopic. This work examined the physicochemical and the nutritional profile of kefir produced in traditional household conditions by fermentation of ultra-high temperature pasteurized (UHT) semi-skimmed cow milk using argentinean kefir grains and compare the stability and nutritional compliance of freshly made and refrigerated kefir, and explored the impact of the intake of this homemade kefir in the skin and in the gastrointestinal symptons of healthy and AD skin volunteers. Additionaly, the acceptance of the kefir drink in a sample of Portuguese consumers was also explored, once kefir is characterized by a unique flavor and aroma and it is not traditionally consumed in Portugal. Results of this research indicate that kefir produced under home use conditions maintains the expected characteristics with respect to the physicochemical parameters and composition, both after fermentation and after two days of refrigerated storage and showed a good acceptance, which supported the protocol adopted. Additionaly, the kefir intervention explored in this study showed an improvement on skin barrier function in both healthy and atopic skin subjects verified only in the respective kefir intake groups. An improvement in the degree of severity of AD was also confirmed for the kefir intake group. This study also showed a higher improvement on functional gastrointestinal symptoms in the kefir intake groups on both healthy and atopic skin subjects. To our knowledge, this was the first human in vivo study to provide information regarding the impact of the intake of homemade kefir on both skin health and functional gastrointestinal symptoms of volunteers with healthy and AD skin. Overall, this work further contributes to the characterization of this food product that is so widely consumed around the world by focusing on kefir that was produced in a typical household setting. Provides valuable information regarding the evaluation of skin health namely atopic skin and opens the possibility to continue the research on the impact of the probiotic kefir on cutaneous health, and its mechanism of action namely via gut-skin axis.