Frailty is an ageing-related syndrome of physiological decline, heightening vulnerability and increasing the risk of adverse health outcomes. Nutritional deficiencies, particularly in vitamins B9, B12, and D, are prevalent among the elderly due to physiological changes and reduced food intake. Research suggests a correlation between low levels of these vitamins and an elevated risk of frailty. Vitamin B9, crucial for DNA synthesis and cell division, shows potential in frailty prevention, although evidence regarding supplementation remains inconclusive. Similarly, vitamin B12, essential for nerve function and red blood cell formation, presents conflicting findings regarding its impact on frailty prevention. Vitamin D, essential for bone health and muscle function, is linked to frailty risk, yet studies on the efficacy of supplementation yield mixed results. The mechanisms involving these vitamins, including their roles in DNA methylation and inflammation regulation, highlight the need for further research to clarify their direct impact on frailty prevention. Maintaining optimal levels of vitamins B9, B12, and D may reduce frailty, but older individuals need a complete approach that includes proper nutrition, physical activity, and other preventive measures.

The fast spread of the coronavirus disease 2019 (COVID-19) epidemic and its high mortality were quickly noticed by the health community. B vitamins are essential micronutrients for the body with antioxidant, anti-inflammatory and immune-regulating properties. The present study can provide a comprehensive picture of the associations between B vitamins and COVID-19 incidence. This study was undertaken on 9189 adult participants of the Yazd Health Study (YaHS) and Taghzieh Mardom-e-Yazd (TAMIZ) study aged 20 to 69 years. Data on dietary intakes were obtained using a validated FFQ. Multivariable logistic regression analysis was used to evaluate the association between B vitamins and COVID-19. Our findings indicated that participants in the fourth quartile of vitamin B5 intake compared with the first quartile had a protective effect against COVID-19 (OR: 0·53, 95 % CI 0·28, 0·99, P-trend = 0·02) after adjustment for all possible confounds in model 3. In addition, participants in the third quartile of vitamin B12 intake compared with the first quartile (OR: 0·63, 95 % CI 0·40, 0·98, P-trend = 0·11) had fewer odds of COVID-19 after full adjustments for confounders. Our findings indicated no significant relationship between dietary intake of vitamin B1, B2, B3, B9 and B-complex and COVID-19. A higher intake of vitamin B5 could reduce the odds of COVID-19 by 47 %, and a moderate intake of vitamin B12 had a protective effect on COVID-19. Although our study has promising results, stronger clinical studies are needed.