Plasma somatomedin activity in vitamin A deficient children

Determinants of GH resistance in malnutrition

States of undernutrition are characterized by GH resistance. Decreased total energy intake, as well as isolated protein-calorie malnutrition and isolated nutrient deficiencies, result in elevated GH levels and low levels of IGF1. We review various states of malnutrition and a disease state characterized by chronic undernutrition - anorexia nervosa - and discuss possible mechanisms contributing to the state of GH resistance, including fibroblast growth factor 21 and Sirtuin 1. We conclude by examining the hypothesis that GH resistance is an adaptive response to states of undernutrition, in order to maintain euglycemia and preserve energy.

Modulation of the growth hormone-insulin-like growth factor (GH-IGF) axis by pharmaceutical, nutraceutical and environmental xenobiotics: an emerging role for xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. A review

The growth hormone-insulin-like growth factor (GH-IGF) axis has gained considerable focus over recent years. One cause of this increased interest is due to a correlation of age-related decline in plasma GH/IGF levels with age-related degenerative processes, and it has led to the prescribing of GH replacement therapy by some practitioners. On the other hand, however, research has also focused on the pro-carcinogenic effects of high GH-IGF levels, providing strong impetus for finding regimes that reduce its activity. Whereas the effects of GH/IGF activity on the action of xenobiotic-metabolizing enzyme systems is reasonably well appreciated, the effects of xenobiotic exposure on the GH-IGF axis has not received substantial review. Relevant xenobiotics are derived from pharmaceutical, nutraceutical and environmental exposure, and many of the mechanisms involved are highly complex in nature, not easily predictable from existing in vitro tests and do not always predict well from in vivo animal models. After a review of the human and animal in vivo and in vitro literature, a framework for considering the different levels of direct and indirect modulation by xenobiotics is developed herein, and areas that still require further investigation are highlighted, i.e. the actions of common endocrine disruptors such as pesticides and phytoestrogens, as well as the role of xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. It is anticipated that a fuller appreciation of the existing human paradigms for GH-IGF axis modulation gained through this review may help explain some of the variation in levels of plasma IGF-1 and its binding proteins in the population, aid in the prescription of particular dietary regimens to certain individuals such as those with particular medical conditions, guide the direction of long-term drug/nutraceutical safety trials, and stimulate ideas for future research. It also serves to warn athletes that using compounds touted as performance enhancing because they promote short-term GH release could in fact be detrimental to performance in the long-run.

Serum vitamin A concentration and the risk of hip fracture among women 50 to 74 years old in the United States: a prospective analysis of the NHANES I follow-up study

BACKGROUND

Recent studies on the association between vitamin A and fracture risk have focused on samples with high vitamin A intake. We analyzed a cohort that was more representative of the overall U.S. population to test the hypothesis that both high and low serum vitamin A concentrations increase the risk of hip fracture.

METHODS

We utilized data on 2799 women who were 50 to 74 years of age from the first National Health and Nutrition Examination Survey Epidemiologic Follow-up Study. There were 172 incident hip fractures during the 22-year follow-up period. Using Cox regression analysis, we analyzed the relation between baseline serum vitamin A (retinol and retinyl esters) concentration, as a continuous variable and by quintiles, and hip fracture risk.

RESULTS

While there was no linear relation between serum vitamin A concentration and the risk of hip fracture in the multivariate analysis (hazard ratio [HR] per SD increase = 1.0; 95% confidence interval [CI]: 0.9 to 1.2), analysis by quintiles revealed a U-shaped relation between serum vitamin A concentration and hip fracture. Fracture risk was significantly higher among subjects in the lowest (HR = 1.9; 95% CI: 1.1 to 3.3) and highest (HR = 2.1; 95% CI: 1.2 to 3.6) quintiles compared with those in the middle quintiles.

CONCLUSION

Both low and high serum vitamin A concentrations may be associated with an increased risk of hip fracture.

Hypovitaminosis A: A model for sudden infant death syndrome

The cause of sudden infant death syndrome (SIDS) is unknown. It is the leading cause of death from age one month to one year in North America. The purpose of this essay is to generate some testable hypotheses as to the cause of SIDS by drawing attention to distinct epidemiological parallels between SIDS and a newly recognized form of enamel hypoplasia, termed localized hypoplasia of the primary canine tooth (LHPC), which has been attributed to vitamin A deficiency. LHPC and SIDS share a common epidemiological profile: winter seasonality, occurrence at 3-5 months, and affecting apparently healthy children, but with increased incidence in socio economically disadvantaged families particularly racial/ethnic minorities (except Hispanics who show a reduced incidence), previously compromised infant health, less prenatal counselling, and less breastfeeding. Vitamin A has pervasive functions throughout the body including bone growth and maintenance of epithelial membranes. It is proposed that SIDS is due in part to hypovitaminosis A through one of several mechanisms: imbalanced basicranial growth producing mechanical constriction on the respiratory nerves passing through the jugular foramen; or through compromised myelination and/or maturation of the brain stem and cranial nerves involved in respiration; or through pharyngeal collapse due to mandibular undergrowth; or dysfunction of hypoxia-sensitive epithelial cells in the trachea. It is recommended that assay of hypoxia-sensitive epithelial cells in the trachea. It is recommended that assay of the retinyl ester content of the liver of SIDS victims be included in autopsy protocol. © 1995 Wiley-Liss, Inc.