A comparison of the effect of supplementation and sunlight exposure on serum vitamin D and parathyroid hormone: A systematic review and meta-analysis

Abstract

Background: Supplementation and getting sunlight exposure are two treatments for vitamin D deficiency. However, studies reported conteroversial findings regarding the efficacy of these two methods.

Objective: To compare the effect of oral vitamin D supplementation with sunlight exposure on serum vitamin D and parathyroid hormone (PTH).

Methods: A computer-based literature search through PubMed, Scopus and Google scholar search engines was conducted until April 2019 to find clinical trials which compared the effect of oral vitamin D supplementation with sunlight exposure on serum vitamin D and PTH. Means for serum 25-hydroxy vitamin D3 (25(OH) D3) and PTH concentration were extracted. A subgroup analysis was used to detect potential sources of inter-study heterogeneity. Mean differences (MD) were analyzed using a random-effects model (the DerSimonian-Laird approach).

Results: A total of seven papers were included in the meta-analysis. Pooled analysis showed that vitamin D supplementation significantly elevated levels of serum 25(OH) D3 in comparison with sunlight exposure (MD: 8.56nmol/l, 95%CI: 4.15, 12.97, T² = 40.32%, H² = 9.45%, P for heterogeneity p?<?0.001). Also, the difference between the effect of vitamin D supplementation and sun exposure was lower in studies which used UVB radiation compared with studies which applied direct sunlight (MD: 11.65?nmol/l, 95%CI: 7.02, 16.28; P for between subgroup heterogeneity = 0.001).

Conclusion: Vitamin D supplementation was more effective than sun exposure at increasing serum 25(OH) D3. The difference between efficacy of vitamin D supplementation and sun exposure was lower in studies which used long-term sun exposure or applied UVB treatment instead of direct sunlight.     

Vitamin D and pancreas: The role of sunshine vitamin in the pathogenesis of diabetes mellitus and pancreatic cancer

Increasing evidence suggests that vitamin D exerts multiple effects beyond bone and calcium metabolism. Vitamin D seems to play a role in pancreatic disease, including type 1 and type 2 diabetes mellitus as well as pancreatic cancer. Vitamin D's immune-modulatory action suggests that it could help prevent type 1 diabetes. In type 2 diabetes, vitamin D may influence β-cell function, insulin sensitivity, and systematic inflammation—all characteristic pathways of that disease. Data from observational studies correlated vitamin D deficiency with risk of type 1 and type 2 diabetes. Prospective and ecological studies of pancreatic cancer incidence generally support a beneficial effect of higher 25-hydroxyvitamin D concentration as well as inverse correlations between UVB dose or exposure and incidence and/or mortality rate of pancreatic cancer. This review discusses the literature regarding vitamin D's role in risk of diabetes and pancreatic cancer. The results to date generally satisfy Hill's criteria for causality regarding vitamin D and incidence of these pancreatic diseases.

However, large randomized, blinded, prospective studies are required to more fully evaluate the potential therapeutic role of vitamin D in preventing pancreatic diseases.     

Effects of supranutritional dietary vitamin E levels on subcellular deposition of α-tocopherol in the muscle and on pork quality

The influence of three levels of vitamin E in the diet of pigs on the subcellular deposition of α-tocopherol in the muscle and on selected quality characteristics of pork meat (oxidative stability of lipids, colour, drip loss, microbial growth) was studied. The content of α-tocopherol in adipose tissue and L. dorsi muscle as well as in mitochondrial and microsomal fractions of the muscle significantly increased (P < 0.05) with increasing levels of dietary vitamin E. The differences in the concentrations of α-tocopherol in the subcellular fractions were evident in the enhanced stability of the membranes when exposed to metmyoglobin/hydrogen peroxide. The beneficial effect of dietary vitamin E on the oxidative stability of pork lipids during the storage of pork chops and ground pork was also demonstrated. Even though lipid oxidation increased in all cases during storage, the pork products from the pigs receiving the highest level of vitamin E (200 IU kg^?1 feed) exhibited the smallest increase in thiobarbituric acid reactive substances. In addition, increased colour stability and decreased drip loss were observed on keeping pork chops, which had been previously frozen for three months, at 4°C under fluoresent light for 10 days. The possible effect of α-tocopherol on membrane fluidity in this context is discussed.     

The effect of co‐administered flavonoids on the metabolism of hesperetin and the disposition of its metabolites in Caco‐2 cell monolayers

Metabolism by phase II enzymes and transport from intestinal cells back into the lumen by ATP binding cassette (ABC) transporters limits the bioavailability of the flavanone hesperetin, the aglycone of hesperidin. This study investigates to what extent other flavonoids modulate the metabolism and transport of hesperetin by characterizing the effect of co‐administrating a series of flavonoids using Caco‐2 cell monolayers in a two‐compartment transwell system. Flavonoids may interfere with hesperetin metabolism and can also inhibit the apically located ABC transporter breast cancer resistance protein (ABCG2) which was previously shown to be responsible for the apical transport of hesperetin metabolites. Co‐exposure of Caco‐2 cell monolayers to hesperetin with specific flavonoids reduced the ratio of apical efflux to basolateral transport of hesperetin metabolites, and in some cases, also reduced the amount of hesperetin metabolites detected extracellularly. As intracellular accumulation of hesperetin metabolites did not account for this decrease, inhibition of metabolism of hesperetin is likely the underlying mechanism for the reduced metabolite formation and excretion. In spite of the reduction in metabolism the amount of hesperetin metabolites transported to the basolateral side significantly increased upon co‐exposure with specific flavonoids and therefore co‐administration of specific flavonoids could be a strategy to improve the bioavailability of hesperetin.     

Flaxseed oil reduces the growth of human breast tumors (MCF‐7) at high levels of circulating estrogen

Flaxseed (FS) has been shown to attenuate mammary tumorigenesis, possibly due to its high α‐linolenic acid (ALA)‐rich oil (FSO) content. This study determined the effect of FSO on the growth of estrogen receptor‐positive human breast tumors (MCF‐7) in ovariectomized athymic mice at high premenopausal‐like estrogen (E2) levels. Mice with established MCF‐7 tumors were fed basal diet (control) or basal diet supplemented with FSO (40 g/kg) for 8 wks. Compared with control, FSO reduced tumor size (33%, p<0.05) and tumor cell proliferation (38%, p<0.05) and increased apoptosis (110%, p<0.001). FSO also reduced human epidermal growth factor receptor‐2 (79%, p<0.05) and epidermal growth factor receptor (57%, p=0.057) expression, which then may have led to a reduction in Akt (54%, p<0.05) and phosphorylation of mitogen‐activated protein kinase (MAPK) to phosphorylated MAPK (pMAPK, 28%, p<0.05). Insulin‐like growth factor‐1 receptor, vascular endothelial growth factor receptor, MAPK and phosphorylated Akt were not affected. FSO increased (p<0.001) serum ALA, eicosapentaenoic acid and docosahexaenoic acid and, in vitro, ALA reduced MCF‐7 cell proliferation (33%, p<0.001). Thus, FSO regressed estrogen receptor‐positive human breast tumorigenesis at high E2 levels via downregulation of the growth factor mediated pathway, likely through its ALA content, and may explain the anti‐tumorigenicity of FS.