Meat as a component of a healthy diet - are there any risks or benefits if meat is avoided in the diet?

Vitamin A deficiency is an endemic nutrition problem throughout much of the developing world, especially affecting the health and survival of infants, young children, and pregnant and lactating women. These age and life-stage groups represent periods when both nutrition stress is high and diet likely to be chronically deficient in vitamin A. Approximately 127 million preschool-aged children and 7 million pregnant women are vitamin A deficient. Health consequences of vitamin A deficiency include mild to severe systemic effects on innate and acquired mechanisms of host resistance to infection and growth, increased burden of infectious morbidity, mild to severe (blinding) stages of xerophthalmia, and increased risk of mortality. These consequences are defined as vitamin A deficiency disorders (VADD). Globally, 4.4 million preschool children have xerophthalmia and 6 million mothers suffer night blindness during pregnancy. Both conditions are associated with increased risk of morbidity and mortality. While reductions of child mortality of 19-54% following vitamin A treatment have been widely reported, more recent work suggests that dosing newborns with vitamin A may, in some settings, lower infant mortality. Among women, one large trial has so far reported a > or = 40% reduction in mortality related to pregnancy with weekly, low-dose vitamin A supplementation. Epidemiologic data on vitamin A deficiency disorders can be useful in planning, designing, and targeting interventions.

https://journals.sagepub.com/doi/pdf/10.1177/15648265030244S204

Vitamin A deficiency disorders in children and women.

Importance of vitamin-A for lung function and development

Objectives/Hypothesis:

In this study we investigated the effectiveness of vitamin A in postinfectious and posttraumatic smell disorders. A possible effect of vitamin A is likely due to the stimulation of regeneration and repair of the peripheral olfactory system.



Study Design:

Double-blind, randomized, placebo-controlled clinical trial.



Methods:

A total of 52 patients (age range, 20–70 years; mean age, 52 years) participated, 26 of whom received placebo (7 male, 19 female) and another 26 verum (8 male, 18 female). A standardized history was obtained in each patient. Olfactory function was measured by means of the Sniffin' Sticks test kit, a validated technique to investigate odor thresholds, odor discrimination, and odor identification. Vitamin A was prescribed at a dose of 10,000 IU per day for 3 months. Follow-up testing was performed on average 5 months after the first investigation.



Results:

Forty-four percent of all patients reported recovery of their sense of smell; 29% of the participants exhibited significant improvement in measured olfactory function. However, there was no significant difference between the outcome of patients receiving verum or placebo.



Conclusions:

The systemic application of vitamin A at a dose of 10,000 IU per day for 3 months does not appear to be useful in the treatment of postinfectious or posttraumatic olfactory loss.

Olfactory function in patients with postinfectious and posttraumatic smell disorders before and after treatment with vitamin A: a double-blind, placebo-controlled, randomized clinical trial

Vitamin A is essential for diverse aspects of life ranging from embryogenesis to the proper functioning of most adult organs. Its derivatives (retinoids) have potent biological activities such as regulating cell growth and differentiation. Plasma retinol-binding protein (RBP) is the specific vitamin A carrier protein in the blood that binds to vitamin A with high affinity and delivers it to target organs. A large amount of evidence has accumulated over the past decades supporting the existence of a cell-surface receptor for RBP that mediates cellular vitamin A uptake. Using an unbiased strategy, this specific cell-surface RBP receptor has been identified as STRA6, a multitransmembrane domain protein with previously unknown function. STRA6 is not homologous to any protein of known function and represents a new type of cell-surface receptor. Consistent with the diverse functions of vitamin A, STRA6 is widely expressed in embryonic development and in adult organ systems. Mutations in human STRA6 are associated with severe pathological phenotypes in many organs such as the eye, brain, heart, and lung. STRA6 binds to RBP with high affinity and mediates vitamin A uptake into cells. This review summarizes the history of the RBP receptor research, its expression in the context of known functions of vitamin A in distinct human organs, structure/function analysis of this new type of membrane receptor, pertinent questions regarding its very existence, and its potential implication in treating human diseases.

The Membrane Receptor for Plasma Retinol-Binding Protein, A New Type of Cell-Surface Receptor

To estimate the role of vitamin A on ciliated cells we investigated whether ciliated cells undergo any alteration during vitamin A deficiency. The epithelia examined include the ciliated cells of the respiratory tract and the ciliated sensory cells of the inner ear, the tongue, and the olfactory cells. This part of the paper will describe the ciliated epithelium of the tracheobronchial tract and its relation to vitamin A status. During vitamin A deficiency a partial loss of ciliae can be observed before any squamous metaplasia (which usually occurs during longer lasting vitamin A deficiency) develops. The scanning electron microscopic data illustrate the altered surface of the epithelium during vitamin A deficiency better than transmission electron microscopy.

Vitamin A and ciliated cells. I. Respiratory epithelia.

Morphological investigation of tongue, olfactory epithelia, trachea and inner ear in vitamin A deficiency are reported. The results support assumptions concerning the loss of sensory function as been at least a secondary effect of alterations of the neighbourhood of the sensory cells caused by vitamin A deficiency. Taste buds are hindered in function by a dense layer of squamous cells and olfaction is decreased by atrophy of the surrounding respiratory epithelium. Inner ear functionality seems to be affected by vitamin A status via a stabilizing effect on the endolymph-perilymph barrier.

U. Wellner

Papers

Vitamin A and ciliated cells. I. Respiratory epithelia.

Vitamin A deficiency and sensory function.