Beta-carotene conversion to vitamin A decreases as the dietary dose increases in humans.

It has been suggested that high doses of beta-carotene limit its conversion to vitamin A, yet this effect has not been well established in humans. A feeding study was conducted in a randomized crossover design in which volunteers consumed 2 doses of deuterium-labeled beta-carotene on 2 occasions, with beta-carotene and vitamin A response assessed by plasma area under the concentration time curve (AUC). Seven volunteers (4 men, 3 women) consumed each of 2 doses of beta-carotene-d8 and provided serial blood samples for 37 d after each dose. beta-Carotene doses were 20 and 40 mg. Plasma beta-carotene-d8 was assessed by HPLC-MS. Plasma retinol (ROH)-d4, which was derived from the beta-carotene-d8, was evaluated by GC-MS after saponification to convert retinyl esters to ROH prior to the formation of the trimethylsilylether. The plasma AUC for beta-carotene-d8 increased 2-fold from the 20-mg dose to the 40-mg dose. The plasma AUC for ROH-d4 increased 36% from the 20-mg dose to the 40-mg dose. These results establish that, in humans, beta-carotene conversion to vitamin A decreases as the dietary dose increases.

Status of plasma folate after folic acid fortification of the food supply in pregnant African American women and the influences of diet, smoking, and alcohol consumption.

BACKGROUND: African American women and socioeconomically challenged women are at risk of compromised folate status and, thus, of folate-related birth defects. Data are limited on circulating folate concentrations in pregnant African American women after folic acid fortification of the food supply was implemented. OBJECTIVE: The objective was to determine the influence of smoking and alcohol consumption on plasma 5-methyltetrahydrofolic acid (5-MTHFA) concentrations in pregnant African American women. DESIGN: Alcohol consumption, smoking exposure, and other characteristics of pregnant African American women reporting to an inner-city antenatal clinic were assessed. At 24 wk of gestation, blood samples and food-frequency intake data were collected. Plasma 5-MTHFA concentrations were determined by liquid chromatography-mass spectrometry for 116 subjects and examined in a correlational study design. RESULTS: Dietary folate and markers of alcohol consumption were positively associated, whereas exposure to smoke was negatively associated with plasma 5-MTHFA. More than one-half of the participants in this population failed to meet the recommended dietary allowance for dietary folate equivalents of 600 microg/d during pregnancy. CONCLUSIONS: Most inner-city African American women are not meeting the recommended dietary allowance for dietary folate during pregnancy, and smoking may further compromise their folate status. Programs to reduce smoking and raise awareness about the importance of folate and multivitamin supplementation during pregnancy need to target this population.

A mass spectrometric validated high-performance liquid chromatography procedure for the determination of folates in foods.

A series of five food reference materials (RM) that had certified values of folate concentrations and five frozen food samples were analyzed for 5-methyltetrahydrofolic acid (5-MTHFA) and folic acid (FA) using a high-performance liquid chromatography (HPLC) method with fluorescence detection that was validated using an HPLC mass spectrometry (MS) method with electrospray ionization. Identical sample specimens were extracted and analyzed in triplicate using both instrumental methods, and a comparison was made of the mean values of 5-MTHFA and FA resulting from these determinations. The analytes were isolated on either a high capacity strong anion exchange solid phase extraction column (HPLC method) or a phenyl Bond Elut column (MS method) prior to analyses. For quantification of the analytes by MS, (13)C-labeled 5-MTHFA and FA were added to samples as internal standards prior to enzymatic digestion and conversion of the polyglutamate forms of 5-MTHFA to the monoglutamic acid. Quantification of FA and 5-MTHFA using the HPLC analysis was carried out using external standards. With the exception of one RM (pig liver), the values established for 5-MTHFA using these methods were highly comparable. In determining the variance associated with these two procedures, it was observed that the mean relative standard error for 5-MTHFA was 12 (range, 2-27%) and 11% (range, 5-25%) for the HPLC and MS methods, respectively. FA was detected in only three of the samples, and the values obtained for it by either method were similar. This is the first paper that describes a mass spectrometric method used in the validation of an HPLC determination of food folates across a wide range of sample matrixes. The comparable values for 5-MTHFA and FA suggest that HPLC analysis with fluorescent detection may be used to accurately quantify folates present in a variety of food matrixes.

Determination of 5-methyltetrahydrofolic acid and folic acid in citrus juices using stable isotope dilution-mass spectrometry.

A stable isotope liquid chromatography-mass spectrometry (LC-MS) method was developed for the quantitative determination of 5-methyltetrahydrofolic acid (5-MTHFA) and folic acid in a variety of commercial citrus juices. Folates were extracted from juices, and the polyglutamyl side chain of 5-MTHFA was cleaved to the monoglutamate form using rat plasma conjugase. The folates were purified on a Bond-Elut column and analyzed by LC-MS with electrospray ionization. The analytes were quantified using the (13)C(5) analogues of 5-MTHFA and folic acid as internal standards. The relative standard error of the method was 3.35% based on replicate analyses (n = 4). This method was then applied to the determination of 5-MTHFA and folic acid in a variety of citrus juices obtained from local supermarkets. It was observed that although both "store" brands and "national" brands of fresh (nonfrozen) juices contained similar concentrations of 5-MTHFA, the "store" brands of fresh juices had on average >5-fold the amount of folic acid compared to the "national" brands. In addition, the "total" folate concentrations were generally below values listed on the food label.

Isolation and characterization of polyphenol type-A polymers from cinnamon with insulin-like biological activity.

The causes and control of type 2 diabetes mellitus are not clear, but there is strong evidence that dietary factors are involved in its regulation and prevention. We have shown that extracts from cinnamon enhance the activity of insulin. The objective of this study was to isolate and characterize insulin-enhancing complexes from cinnamon that may be involved in the alleviation or possible prevention and control of glucose intolerance and diabetes. Water-soluble polyphenol polymers from cinnamon that increase insulin-dependent in vitro glucose metabolism roughly 20-fold and display antioxidant activity were isolated and characterized by nuclear magnetic resonance and mass spectroscopy. The polymers were composed of monomeric units with a molecular mass of 288. Two trimers with a molecular mass of 864 and a tetramer with a mass of 1152 were isolated. Their protonated molecular masses indicated that they are A type doubly linked procyanidin oligomers of the catechins and/or epicatechins. These polyphenolic polymers found in cinnamon may function as antioxidants, potentiate insulin action, and may be beneficial in the control of glucose intolerance and diabetes.