Seasonal variation of vitamin A (retinol) status in older men and women

Retinol Binding Protein, Sunlight Hours, and the Influenza Virus-Specific Immune Response

Healthy pediatric immune responses depend on adequate vitamin A and D levels. Relationships between solar ultraviolet B (UVB) radiation and vitamin D are well understood, while relationships between sunlight, vitamin A, and its serum escort, retinol binding protein (RBP), are not. A pediatric clinical study enrolled 2–8-year-old children at various times between September 2016 and March 2017, inclusive, in Memphis, Tennessee. A serum sample from each child was then assayed to examine the influence of season on vitamin levels. We found that RBP and RBP/retinol molar ratios decreased in winter months and RBP/retinol ratios correlated positively with the average daily sunlight hours per month. A food frequency questionnaire given to parents/guardians indicated a shift in dietary intake from plant-based foods to animal-based foods by children between winter and spring months. This translated to higher retinol and zinc (integral to RBP–transthyretin–retinol complexes) in the spring, perhaps explaining the seasonal influence on RBP/retinol. RBP and retinol were associated positively with IgG/IgM and IgA/IgM ratios. RBP and retinol, but not 25(OH)D, also correlated positively with influenza virus-specific antibodies. Retinol correlated negatively, while 25(OH)D correlated positively, with certain serum cytokine/chemokine levels. Significant differences in 25(OH)D, immunoglobulin ratios, and cytokines/chemokines were observed between black and white children. In sum, seasonal changes in dietary foods rich in retinol and zinc may have influenced RBP levels, which in turn influenced innate and adaptive immune responses. Results encourage routine monitoring and reporting of season, RBP, and vitamin levels in future clinical studies, as seasons may affect sunlight exposures, diet, vitamin levels, and immune protection against infectious disease.

Effects of seasonal and physiological variations on the serum chemistry, vitamins and thyroid hormone concentrations in sheep

The aim of this study was to investigate the possible effects of the reproductive status and seasonal variations on the serum chemistry and vitamin status and their relationships with the thyroid hormones in Sakiz-Awassi crossbreed sheep. The sheep (n = 34) were divided into two groups. The first group (n = 22) was mated; the second group (n = 12) was not mated. Their serum samples were collected four times a year at the each season and under reproductive status. The periods are 1, early pregnancy (October); 2, late pregnancy (January); 3, lactation (April); and 4, dry season (July). The results of this study indicated that (1) total protein (TP), globulin, cholesterol, creatinine, uric acid and T4/T3 vary with reproductive status but not seasonal variations; (2) alanine aminotransferase, T4, fT4 concentrations in serum vary only with reproductive status; (3) the urea, creatine kinase, lactate dehydrogenase, alkaline phosphatase, aspartate aminotransferase, amylase, albumin, triglyceride, VLDL, Vit A-E, T3 and fT3 concentration could vary with both reproductive status and seasonal variations; (4) the glucose, gamma-glutamyl transpeptidase, folate concentrations were altered neither season of the year nor the reproductive status; (5) a single reference interval for folate, gamma-glutamyl transpeptidase (GGT), glucose, TP, globulin, cholesterol, creatinine, uric acid and T4/T3 can be used for both mated and non-mated sheep because of no differences were found due to the reproductive status. Taking the results together suggests that reproductive status and seasonal variations have to be taken into consideration for a correct interpretation of the serum chemistry values of sheep. Nutritional supplements are required for sheep during certain periods to avoid a decline of their performance, which would then represent consequent economic, loses.

Biological variation of retinoids in man

This investigation was undertaken to assess biological variation, especially the within-subject variations of all-trans retinoic acid, 13-cis retinoic acid and retinol in human serum. Diurnal variation and variation over a week, a month and a year were studied in 11 males (aged 21-54 years) and 17 females (aged 22-63 years), all subjectively healthy. We found no diurnal variation with the exception of all-trans retinoic acid, which had maximal concentrations at noon irrespective of food intake. Seasonal variations were marginal. Both all-trans and 13-cis retinoic acids had fairly high within-subject (13.1%, and 12.6%, respectively) and between-subject coefficients of variation (15.9% and 21.0%, respectively), while the within-subject CV of retinol was less (5.6%, with a between-subject CV of 21.1%). Thus, the indices of individuality were < 1 for all retinoids. The critical differences between two consecutive samples were < 40% for the retinoic acids and < 20% for retinol. Women had higher all-trans retinoic acid concentrations in serum (5.1 nmol/L vs. 4.5 nmol/L), lower 13-cis retinoic acid concentrations (4.5 nmol/L vs. 5.5 nmol/L) and lower retinol concentrations in serum (2.1 micromol/L vs. 2.5 micromol/L) than men. Thus, samples for retinoid determinations should be drawn in the morning and evaluated using separate gender reference intervals.

Seasonal variation in glucocorticoid receptor binding characteristics in human mononuclear leucocytes

OBJECTIVE

Glucocorticoid sensitivity varies between individuals and between tissues in the same individual. Although some of this variation is explained by the activity of the 11 beta-hydroxysteroid dehydrogenase enzymes, the possibility that glucocorticoid receptor sensitivity is modulated remains unexplored. This study examined glucocorticoid receptor binding in leucocytes and assessed the effects of seasonal hormonal variation on receptor binding.

PATIENTS AND MEASUREMENTS

Two populations were studied. In the first, 318 healthy subjects were studied over 2 years with a single measurement of receptor binding made on each. In the second study nine healthy male subjects each had receptor binding measurements made at 3-week intervals over 1 year.

RESULTS

In both populations there was significant seasonal variation in receptor binding. In the first population Kd for dexamethasone was highest in November and lowest in July (8.37 +/- 0.5 nmol/l vs. 1.58 +/- 0.7, mean +/- SEM P < 0.00001) and the number of receptor sites per leucocyte was highest in January and lowest in June (10 440 +/- 580 vs. 4969 +/- 302, P < 0.00001). In multivariate analysis, climate was the main determinant for both Kd and the number of receptor sites per cell: increases in day length and environmental temperature reduced Kd and the number of receptor sites per cell. Co-incubation with physiological concentrations of melatonin raised Kd without affecting receptor number. Co-incubation with forskolin lowered Kd suggesting that melatonin might act through the ML1 receptor class by inhibiting adenylyl cyclase. No correlations were found with 0900 h plasma cortisol.

CONCLUSIONS

The results suggest that the glucocorticoid receptor might be modulated by season. Melatonin might mediate part of these effects. The lack of correlation with cortisol suggests that it is not an important determinant of receptor binding and that leucocyte receptors are regulated differently from central receptors.

Antioxidant potentials of vitamin A and carotenoids and their relevance to heart disease

Despite being one of the first vitamins to be discovered, the full range of biological activities for vitamin A remains to be defined. Structurally similar to vitamin A, carotenoids are a group of nearly 600 compounds. Only about 50 of these have provitamin A activity. Recent evidence has shown vitamin A, carotenoids and provitamin A carotenoids can be effective antioxidants for inhibiting the development of heart disease. Vitamin A must be obtained from the diet: green and yellow vegetables, dairy products, fruits and organ meats are some of the richest sources. Within the body, vitamin A can be found as retinol, retinal and retinoic acid. Because all of these forms are toxic at high concentrations, they are bound to proteins in the extracellular fluids and inside cells. Vitamin A is stored primarily as long chain fatty esters and as provitamin carotenoids in the liver, kidney and adipose tissue. The antioxidant activity of vitamin A and carotenoids is conferred by the hydrophobic chain of polyene units that can quench singlet oxygen , neutralize thiyl radicals and combine with and stabilize peroxyl radicals. In general, the longer the polyene chain, the greater the peroxyl radical stabilizing ability. Because of their structures, vitamin A and carotenoids can autoxidize when O2 tension increases, and thus are most effective antioxidants at low oxygen tensions that are typical of physiological levels found in tissues. Overall, the epidemiological evidence suggests that vitamin A and carotenoids are important dietary factors for reducing the incidence of heart disease. Although there is considerable discrepancy in the results from studies in humans regarding this relationship, carefully controlled experimental studies continue to indicate that these compounds are effective for mitigating and defending against many forms of cardiovascular disease. More work, especially concerning the relevance of how tissue concentrations, rather than plasma levels, relate to the progression of tissue damage in heart disease is required. This review assembles information regarding the basic structure and metabolism of vitamin A and carotenoids as related to their antioxidant activities. Epidemiological, intervention trials and experimental evidence about the effectiveness of vitamin A and carotenoids for reducing cardiovascular disease is also reviewed.

Vitamin supplementation therapy in the elderly

Vitamin supplementation in large dosages is increasingly common in the older population. Often, such supplementation is used in an attempt to improve an individual's health status. There have been claims that the effects of vitamins halt the normal aging process or prevent and cure disease. However, several recent studies have failed to demonstrate the efficacy of vitamin supplementation in preventing several types of cancer. In moderate dosages, supplementation with vitamin E (tocopherols) shows promise as a lipid antioxidant, and may reduce the risk of coronary heart disease. However, before vitamin E becomes an accepted medical therapy, further long term studies must be undertaken to examine the safety and efficacy of such therapy. An adequate intake of vitamins should be ensured by adherence to a well balanced diet. However, the elderly are prone to circumstances that may prevent them from eating a balanced diet. In addition, there are several age-related medical conditions that may predispose individuals to dietary and vitamin deficiencies. To prevent vitamin deficiency diseases and their associated morbidity, modest vitamin supplementation may be necessary. However, supplementation should be reserved for individuals with documented deficiency or who are at risk of developing such deficiencies, especially those who are homebound or institutionalised. Vitamins taken in large dosages should be considered as drugs. These medicines, which are obtainable over-the-counter, should be carefully regulated to prevent toxicity.

Influence of vitamin D and retinoids on the gammacarboxylation of osteocalcin in human osteosarcoma MG63 cells

Osteocalcin (OC) is a bone matrix protein, synthesized by osteoblasts, which contains three residues of gammacarboxyglutamic acid (GLA). A fraction of circulating OC, which is not fully carboxylated and does not bind to hydroxyapatite, is called undercarboxylated OC (ucOC). In elderly institutionalized women, we have shown an increase of circulating ucOC level which may result not only from vitamin K deficiency but also from vitamin D deficiency (Szulc et al., J Clin Invest 91:1769; 1993). This intriguing finding prompted us to study the effect of vitamin D on the secretion of ucOC by osteoblastic cells in vitro in the presence of warfarin, an inhibitor of gammacarboxylation of GLA-containing proteins. The potential influence of retinoic acid (RA) was also studied, because its mechanism of action involves pathways that are similar to vitamin D. In the presence of warfarin (0.05 microg/mL), 1alpha,25(OH)2D (10(-8)-10(-6) mol/L) decreased dose dependently ucOC secretion by human osteosarcoma MG63 cells (from 3.87 +/- 0.96 to 2.12 +/- 0.13 ng/10(6) cells). When expressed as a fraction of total OC, secretion ucOC decreased from 47.4 +/- 1.4% to 24.8 +/- 3.2% in the MG63 cells. The secretion of total OC was stimulated by RA and by Ro 13-7410, which is a specific ligand of retinoic acid receptor (RAR), but not by 9-cis retinoic acid (9-cisRA), which is a physiologic ligand of retinoid X receptor (RXR). RA and Ro 13-7410 decreased ucOC secretion and ucOC% in warfarin-treated MG63 cells (RA: from 50.4 +/- 13.3% to 13.5 +/- 2.8%; Ro 13-7410: from 28.4 +/- 8.2% to 11.3 +/- 8.4%). 9-cisRA had no effect on OC gammacarboxylation. These results show that vitamin D, RA, and Ro 13-7410, but not 9-cisRA, may modify the gammacarboxylation of OC in human MG63 cells.