Vitamin D and the metabolic syndrome.

Vitamin D is essential in bone mineralization and calcium homeostasis, and an increasing body of evidence suggests that vitamin D may be important for maintaining extraskeletal health, including having beneficial effects on cardiometabolic outcomes. Vitamin D deficiency is widespread, but the role of vitamin D in the metabolic syndrome is not fully elucidated. In this review we summarize data from observational studies and randomized controlled trials on the relation between vitamin D and the metabolic syndrome and its components. A large number of observational studies suggest a relationship between low levels of 25(OH)D and the metabolic syndrome or its individual clinical features. Randomized controlled trials of vitamin D supplementation addressing aspects of the metabolic syndrome have yielded inconsistent results, and many studies suffer from methodological limitations. There is an urgent need for large, well-designed randomized controlled trials with relevant endpoints. Until definitive results from such studies are available, caution should be taken towards the use of vitamin D-supplementation for disorders other than musculoskeletal system. New molecular biological techniques elucidating the interaction between the active vitamin D derivatives and target genes represent a promising approach to more precise knowledge about new biomedical function, which also might shed light on the complex metabolic syndrome.

Gene-nutrient interactions on the phosphoenolpyruvate carboxykinase influence insulin sensitivity in metabolic syndrome subjects.

BACKGROUND & AIMS: Genetic background may interact with habitual dietary fat composition, and affect development of the metabolic syndrome (MetS). The phosphoenolpyruvate carboxykinase gene (PCK1) plays a significant role regulating glucose metabolism, and fatty acids are key metabolic regulators, which interact with transcription factors and influence glucose metabolism. We explored genetic variability at the PCK1 gene locus in relation to degree of insulin resistance and plasma fatty acid levels in MetS subjects. Moreover, we analyzed the PCK1 gene expression in the adipose tissue of a subgroup of MetS subjects according to the PCK1 genetic variants. METHODS: Insulin sensitivity, insulin secretion, glucose effectiveness, plasma concentrations of C-peptide, fatty acid composition and three PCK1 tag-single nucleotide polymorphisms (SNPs) were determined in 443 MetS participants in the LIPGENE cohort. RESULTS: The rs2179706 SNP interacted with plasma concentration of n - 3 polyunsaturated fatty acids (n - 3 PUFA), which were significantly associated with plasma concentrations of fasting insulin, peptide C, and HOMA-IR. Among subjects with n - 3 PUFA levels above the population median, carriers of the C/C genotype exhibited lower plasma concentrations of fasting insulin (P = 0.036) and HOMA-IR (P = 0.019) as compared with C/C carriers with n - 3 PUFA below the median. Moreover, homozygous C/C subjects with n - 3 PUFA levels above the median showed lower plasma concentrations of peptide C as compared to individuals with the T-allele (P = 0.006). Subjects carrying the T-allele showed a lower gene PCK1 expression as compared with carriers of the C/C genotype (P = 0.015). CONCLUSIONS: The PCK1 rs2179706 polymorphism interacts with plasma concentration of n - 3 PUFA levels modulating insulin resistance in MetS subjects.

Impact of dietary fat quantity and quality on skeletal muscle fatty acid metabolism in subjects with the metabolic syndrome.

Insulin resistance is characterized by disturbances in lipid metabolism in skeletal muscle. Our aim was to investigate whether gene expression and fatty acid (FA) profile of skeletal muscle lipids are affected by diets differing in fat quantity and quality in subjects with the metabolic syndrome (MetS) and varying degrees of insulin sensitivity. 84 subjects (age 57.3±0.9 y, BMI 30.9±0.4 kg/m(2), 42 M/42 F) were randomly assigned to one of four iso-energetic diets: high-SFA (HSFA); high-MUFA (HMUFA) or two low-fat, high-complex carbohydrate diets, supplemented with 1.24 g/day of long-chain n-3 PUFA (LFHCCn-3) or control oil (LFHCC) for 12 weeks. In a subgroup of men (n=26), muscle TAG, DAG, FFA and phospholipid contents were determined including their fractional synthetic rate (FSR) and FA composition at fasting and 4h after consumption of a high-fat mixed-meal, both pre- and post-intervention. Genes involved in lipogenesis were downregulated after HMUFA (mean fold change -1.3) and after LFHCCn-3 (fold change -1.7) in insulin resistant subjects (< median of (S(I))), whereas in insulin sensitive subjects (>median of insulin sensitivity) the opposite effect was shown (fold change +1.6 for both diets). HMUFA diet tended to decrease FSR in TAG (P=.055) and DAG (P=.066), whereas the LFHCCn-3 diet reduced TAG content (P=.032). In conclusion, HMUFA and LFHCCn-3 diets reduced the expression of the lipogenic genes in skeletal muscle of insulin resistant subjects, whilst HMUFA reduced the fractional synthesis rate of DAG and TAG and LFHCC n-3 the TAG content. Our data indicate that these diets may reduce muscle fat accumulation by affecting the balance between FA synthesis, storage and oxidation.

A low-fat high-carbohydrate diet supplemented with long-chain n-3 PUFA reduces the risk of the metabolic syndrome.

OBJECTIVE: Dietary changes are major factor in determining cardiovascular risk. We assessed the effects of isoenergetic diets with different fat quantity and quality on the incidence and regression of the metabolic syndrome (MetS) from the LIPGENE project. METHODS AND DESIGN: Clinical intervention study: the patients (n=337) were randomly assigned to one of four diets for 12 weeks each: two high fat diets, one rich in saturated fat (HSFA) and the other rich in monounsaturated fat (HMUFA), and two low fat diets, one high in complex carbohydrates (LFHCC) supplemented with 1.24g/day of long-chain n-3 polyunsaturated fatty acids (LFHCC n-3) and the other LFHCC diet with placebo (LFHCC). MEASUREMENTS: the effects on MetS risk criteria were recorded before and after the intervention period. RESULTS: An enlarged waist circumference (≥88cm for women and ≥102cm for men) was present among 95% of the participants, 88% had elevated blood pressure (>130/85mm Hg or antihypertensive drugs), 77% had elevated fasting plasma glucose (≥5.55mmol/L), 51% were hypertriacylglycerolemic (≥1.7mmol/L), and 72% had low HDL cholesterol (<1.0mmol/L for men, and <1.3mmol/L for women). The prevalence of enlarged waist circumference, hypertension and hypertriacylglycerolemia were reduced after the LFHCC n-3 diet (p<0.05). Thus the prevalence of MetS fell by 20.5% after LFHCC n-3 diet compared with the HSFA (10.6%), HMUFA (12%) diet or LFHCC (10.4%) diets (p<0.028). CONCLUSIONS: The consumption of a low-fat high-carbohydrate supplemented with n-3 diet reduced the risk of MetS as compared with isoenergetic high-fat (HSFA and HMUFA) and LFHCC diets.

NOS3 gene polymorphisms are associated with risk markers of cardiovascular disease, and interact with omega-3 polyunsaturated fatty acids.

OBJECTIVE: Omega-3 polyunsaturated fatty acids (n-3 PUFA) may protect against the development of cardiovascular disease (CVD). Genotype at key genes such as nitric oxide synthase (NOS3) may determine responsiveness to fatty acids. Gene-nutrient interactions may be important in modulating the development of CVD, particularly in high-risk individuals with the metabolic syndrome (MetS). METHODS: Biomarkers of CVD risk, plasma fatty acid composition, and NOS3 single nucleotide polymorphism (SNP) genotype (rs11771443, rs1800783, rs1800779, rs1799983, rs3918227, and rs743507) were determined in 450 individuals with the MetS from the LIPGENE dietary intervention cohort. The effect of dietary fat modification for 12 weeks on metabolic indices of the MetS was determined to understand potential NOS3 gene-nutrient interactions. RESULTS: Several markers of inflammation and dyslipidaemia were significantly different between the genotype groups. A significant gene-nutrient interaction was observed between the NOS3 rs1799983 SNP and plasma n-3 PUFA status on plasma triacylglycerol (TAG) concentrations. Minor allele carriers (AC+AA) showed an inverse association with significantly higher plasma TAG concentrations in those with low plasma n-3 PUFA status and vice versa but the major allele homozygotes (CC) did not. Following n-3 PUFA supplementation, plasma TAG concentrations of minor allele carriers of rs1799983 were considerably more responsive to changes in plasma n-3 PUFA, than major allele homozygotes. CONCLUSIONS: Carriers of the minor allele at rs1799983 in NOS3 have plasma TAG concentrations which are more responsive to n-3 PUFA. This suggests that these individuals might show greater beneficial effects of n-3 PUFA consumption to reduce plasma TAG concentrations.

Dietary fat modifications and blood pressure in subjects with the metabolic syndrome in the LIPGENE dietary intervention study.

Hypertension is a key feature of the metabolic syndrome. Lifestyle and dietary changes may affect blood pressure (BP), but the knowledge of the effects of dietary fat modification in subjects with the metabolic syndrome is limited. The objective of the present study was to investigate the effect of an isoenergetic change in the quantity and quality of dietary fat on BP in subjects with the metabolic syndrome. In a 12-week European multi-centre, parallel, randomised controlled dietary intervention trial (LIPGENE), 486 subjects were assigned to one of the four diets distinct in fat quantity and quality: two high-fat diets rich in saturated fat or monounsaturated fat and two low-fat, high-complex carbohydrate diets with or without 1.2 g/d of very long-chain n-3 PUFA supplementation. There were no overall differences in systolic BP (SBP), diastolic BP or pulse pressure (PP) between the dietary groups after the intervention. The high-fat diet rich in saturated fat had minor unfavourable effects on SBP and PP in males.