The acute effects of different macronutrients on the secretion of glucagon-like peptide-1(7-36)amide (GLP-1(7-36)amide) and glucose-dependent insulinotropic polypeptide (GIP) were compared in healthy human subjects. Circulating levels of the two hormones were measured over a 24-h period during which subjects consumed a mixed diet. In the first study, eight subjects consumed three equicaloric (375 kcal) test meals of carbohydrate, fat and protein. Small increases in plasma GLP-1(7-36) amide were found after all meals. Levels reached a maximum 30 min after the carbohydrate and 150 min after the fat load. Ingestion of both carbohydrate and fat induced substantial rises in GIP secretion, but the protein meal had no effect. In a second study, eight subjects consumed 75 g glucose or the equivalent portion of complex carbohydrate as boiled brown rice or barley. Plasma GIP, insulin and glucose levels increased after all three meals, the largest increase being observed following glucose and the smallest following the barley meal. Plasma GLP-1(7-36)amide levels rose only following the glucose meal. In the 24-h study, plasma GLP-1(7-36)amide and GIP concentrations were increased following every meal and remained elevated throughout the day, only falling to fasting levels at night. The increases in circulating GLP-1(7-36)amide and GIP levels following carbohydrate or a mixed meal are consistent with their role as incretins. The more sustained rises observed in the daytime during the 24-h study are consistent with an anabolic role in lipid metabolism.

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The normal degree of intra- and interindividual variation in gene transcription profiles of healthy human tissues has not been extensively investigated. In the study described here, microarrays were employed to analyze gene transcription in peripheral blood mononuclear cells prepared from serial blood samples that had been obtained, at weekly intervals, from apparently healthy human volunteers. Transcript levels for the majority of genes examined were found to be remarkably consistent within samples from a single donor. Conversely, marked differences were observed in samples obtained from different donors. Genes that exhibited differential expression dependent on sex, age, body mass index, and the presence of varying proportions of different leukocyte subsets were identified. These results emphasize the important contributions of genetic and environmental factors, as well as varying representation of different cell types, in determining the overall gene transcriptional profiles of human tissues. However, the study also provides evidence that, within an individual, the gene transcription profiles of sampled tissues can be comparatively stable over time.

There are conflicting views in the literature as to whether vitamin D and vitamin D are equally effective in increasing and maintaining serum concentrations of 25-hydroxyvitamin D [25(OH)D], particularly at lower doses of vitamin D. We aimed to investigate whether vitamin D or vitamin D fortified in juice or food, at a relatively low dose of 15 μg/d, was effective in increasing serum total 25(OH)D and to compare their respective efficacy in South Asian and white European women over the winter months within the setting of a large randomized controlled trial. A randomized, double-blind, placebo-controlled food-fortification trial was conducted in healthy South Asian and white European women aged 20-64 y ( = 335; Surrey, United Kingdom) who consumed placebo, juice supplemented with 15 μg vitamin D, biscuit supplemented with 15 μg vitamin D, juice supplemented with 15 μg vitamin D, or biscuit supplemented with 15 μg vitamin D daily for 12 wk. Serum 25(OH)D was measured by liquid chromatography-tandem mass spectrometry at baseline and at weeks 6 and 12 of the study. Postintervention in the 2 ethnic groups combined, both the vitamin D biscuit and the vitamin D juice groups showed a significantly greater absolute incremental change (Δ) in total 25(OH)D when compared with the vitamin D biscuit group [Δ (95% CI): 15.3 nmol/L (7.4, 23.3 nmol/L) ( < 0.0003) and 16.0 nmol/L (8.0, 23.9 nmol/L) ( < 0.0001)], the vitamin D juice group [Δ (95% CI): 16.3 nmol/L (8.4, 24.2 nmol/L) ( < 0.0001) and 16.9 nmol/L (9.0, 24.8 nmol/L) ( < 0.0001)], and the placebo group [Δ (95% CI): 42.3 nmol/L (34.4, 50.2 nmol/L) ( < 0.0001) and 42.9 nmol/L (35.0, 50.8 nmol/L) ( < 0.0002)]. With the use of a daily dose of vitamin D relevant to public health recommendations (15 μg) and in vehicles relevant to food-fortification strategies, vitamin D was more effective than vitamin D in increasing serum 25(OH)D in the wintertime. Vitamin D may therefore be a preferential form to optimize vitamin D status within the general population. This trial was registered at www.controlled-trials.com as ISRCTN23421591.