Biomedical subjects

R Hovenier

Publications and source records attributed to R Hovenier.

7 recordsLinked to original sources

PubMed1998

Effects of the flavonoids quercetin and apigenin on hemostasis in healthy volunteers: results from an in vitro and a dietary supplement study.

Intake of dietary flavonols and flavones was inversely associated with risk for cardiovascular disease in several epidemiologic studies. This may have been due to effects on hemostasis because flavonoids have been reported to inhibit platelet aggregation in vitro. We indeed found that 2500 micromol/L of the flavonol quercetin and the flavone apigenin significantly inhibited collagen- and ADP-induced aggregation in platelet-rich plasma and washed platelets by approximately 80-97%. However, lower concentrations, such as might occur in vivo, had no effect. To test this in vivo we fed 18 healthy volunteers 220 g onions/d providing 114 mg quercetin/d, 5 g dried parsley/d providing 84 mg apigenin/d, or a placebo for 7 d each in a randomized crossover experiment with each treatment period lasting 2 wk. Onion consumption raised mean plasma quercetin concentrations to 1.5 micromol/L; plasma apigenin could not be measured. No significant effects of onions or parsley were found on platelet aggregation, thromboxane B2 production, factor VII, or other hemostatic variables. We conclude that the antiaggregatory effects of flavonoids seen in vitro are due to concentrations that cannot be attained in vivo. Effects of dietary flavonols and flavones on cardiovascular risk are possibly not mediated by hemostatic variables.

Adult↗

PubMed1997

Diterpenes from coffee beans decrease serum levels of lipoprotein(a) in humans: results from four randomised controlled trials.

OBJECTIVE: Unfiltered coffee raises serum LDL cholesterol in humans, owing to the presence of the diterpenes cafestol and kahweol. Norwegians with a chronic high intake of unfiltered coffee also has elevated serum levels of lipoprotein(a), an LDL-like particle which is insensitive toward dietary interventions. We now experimentally studied the influence of coffee diterpenes on lipoprotein(a) levels. DESIGN: Four randomised controlled trials. SUBJECTS: Healthy, normolipidemic volunteers. INTERVENTIONS: Coffee, coffee oil, and pure diterpenes for 4-24 weeks. MAIN OUTCOME MEASURES: The circulating level of lipoprotein(a). RESULTS: In 22 subjects drinking five to six strong cups of cafetiere coffee per day, the median fall in lipoprotein(a) was 1.5 mg/dL after two months (P = 0.03), and 0.5 mg/dL after half a year (P > 0.05), relative to 24 filter coffee drinkers. Coffee oil doses equivalent to 10-20 cups of unfiltered coffee reduced lipoprotein(a) levels by up to 5.5 mg/dL (P < 0.05) in two separate trials (n = 12-16 per group). A purified mixture of cafestol and kahweol, as well as cafestol alone, were also effective in reducing Lp(a) levels (n = 10). Averaged over the four trials, each 10 mg/d of cafestol (plus kahweol)--the amount present in two to three cups of cafetiere coffee--decreased Lp(a) levels by 0.5 mg/dL or 4% from baseline values after four weeks (n = 63). CONCLUSIONS: Coffee diterpenes are among the few dietary exceptions shown to influence serum lipoprotein(a) levels. However, the Lp(a)-reducing potency of coffee diterpenes may subside in the long run, and their adverse side effects preclude their use as lipoprotein(a)-reducing agents.

Adult↗

PubMed1996

Chronic consumers of boiled coffee have elevated serum levels of lipoprotein(a).

OBJECTIVES: Lipoprotein(a) consists of an LDL-particle attached to apolipoprotein(a), which is made by the liver. Diterpenes present in boiled coffee raise serum levels of LDL cholesterol and of the liver enzyme alanine aminotransferase in man. We investigated the association between intake of boiled coffee and serum levels of lipoprotein(a). DESIGN, SETTING AND SUBJECTS: Healthy Norwegians 40-42 years of age, who habitually consumed five or more cups of boiled coffee per day (n = 150) were compared with matched filter coffee consumers (n = 159) in a cross-sectional study, as part of the Norwegian National Health Screening in 1992. RESULTS: The median lipoprotein(a) level was 13.0 mg dL-1 (10th and 90th percentile: 2.5 and 75.0 mg dL-1, respectively) on boiled and 7.9 mg dL-1 (10th and 90th percentile: 1.9 and 62.5 mg dL-1, respectively) on filter coffee (P = 0.048). Means +/- SE were 25.8 +/- 2.4 mg dL-1 and 19.6 +/- 2.0 mg dL-1, respectively (P = 0.04). Although not statistically significant, subjects consuming nine or more cups of coffee per day had higher lipoprotein(a) levels than those drinking five to eight cups per day in both coffee groups. CONCLUSION: Chronic consumers of unfiltered, boiled coffee have higher serum levels of lipoprotein(a) than filter coffee drinkers.

Adult↗

PubMed1996

Supplemental vitamin A enhances the recovery from iron deficiency in rats with chronic vitamin A deficiency.

Studies with anaemic children and pregnant women from areas where vitamin A deficiency is endemic have shown a beneficial effect on Fe status of supplemental vitamin A in addition to Fe supplementation. This suggests a relationship between vitamin A and Fe status, which we attempted to mimic in rats with anaemia and chronic vitamin A deficiency. Male rats were fed on Fe-adequate diets (35 mg Fe/kg) containing different levels of vitamin A (1200, 450, 150, 75 and 0 retinol equivalent (RE)/kg feed) until they were 5 weeks old. These diets were identical to the diets fed to their mothers. Then the young male rats were transferred to diets containing the same levels of vitamin A but no added Fe. After another 2 weeks the rats were repleted with Fe (35 mg/kg feed) without or with vitamin A to a level of 1200 RE/kg feed. Increased vitamin A intake by the groups previously fed on diets with either 0 or 75 RE/kg produced a reduction in blood haemoglobin concentration, packed cell volume and erythrocyte count. In the group which had been fed on the diet without vitamin A, supplemental vitamin A raised mean cell volume, plasma Fe concentration and total Fe-binding capacity. Vitamin A supplementation during the period of Fe repletion produced a decrease in splenic and tibia Fe concentration, the effect being greater with increasing severity of previous vitamin A deficiency. The paradoxical effect of supplemental vitamin A on haemoglobin, packed cell volume and erythrocyte count can be explained by a decrease in the degree of haemoconcentration. Thus, the positive effect of supplemental vitamin A seen in humans is also observed with rats under controlled experimental conditions. We speculate that supplemental vitamin A during Fe repletion contributes to optimum erythropoiesis and Fe mobilization when baseline vitamin A status is impaired.

Anemia, Iron-Deficiency↗

PubMed1995

Evaluation of a two-generation rat model for vitamin A deficiency and the interrelationship with iron metabolism.

In order to induce a range of vitamin A-deficient states in young growing rats and to study the effect of vitamin A deficiency on Fe status, we designed the following two-generation experiment. Dams were fed on diets with one of five vitamin A levels from 2 weeks before and throughout pregnancy and lactation. The pups received the same diets as their mothers both before and after weaning. The five dietary levels of vitamin A were 1200, 450, 150, 75 and 0 retinol equivalents/kg feed. Vitamin A intake did not affect reproduction outcome, nor were body and liver weights of the pups affected when they were 3.5 weeks old. Male pups with normal vitamin A status had higher plasma retinol levels than female pups. Vitamin A status of the offspring was affected from 3.5 weeks onwards. Body and liver weights were decreased in the male pups given the lowest dietary vitamin A levels from week 6.5 onwards but not in the female pups. Fe status was marginally affected. Haemoglobin levels were increased and total Fe-binding capacity was decreased in the groups given no dietary vitamin A at week 9.5. Splenic Fe was increased only in the male pups given the lowest levels of dietary vitamin A. However, as a whole, Fe status was only mildly affected and subject to considerable variation. We conclude that the two-generation rat model described here is not suitable for studying effects of vitamin A deficiency on Fe metabolism.

Animals↗

PubMed1993

Economic values of optimum traits: the example of meat quality in pigs.

In this paper a method is outlined to derive marginal-income functions and to calculate economic values for traits with an intermediate optimum such as meat-quality traits. A normal distribution of the quality trait was assumed, but the method can be used for other distributions as well. The parameters necessary to use this method are distribution of the quality trait, population mean and the standard deviation of the quality trait, optimum range, and price differences between products within and outside the optimum range. Especially, the optimum range for the quality trait and the price differences to be used have to be derived from consumer and processing research. Some alternative methods that can be used for selection on quality traits, such as restricted selection index, desired-gains index, and indices based on a quadratic aggregate genotype, are discussed.

Animals↗

PubMed1993

Repeatability of taste panel tenderness scores and their relationships to objective pig meat quality traits.

Repeatabilities of 12 meat quality measurements were calculated as a value for the accuracy of those measurements. Sixty-four Duroc and Dutch Yorkshire boars and gilts were slaughtered during 8 wk. The repeatabilities between carcass halves within animals were .53 for repeated taste panel tenderness scores based on 12.4 observations of different panelists per mean, .08 for two repeated tenderness scores of different panelists within one animal, .50 for two repeated tenderness scores of one panelist within one animal, and 41 for repeated measurements of maximum shear force. Repeatabilities of other meat quality traits ranged from .29 for cooking loss to .76 for the Minolta L* color coordinate. The phenotypic correlation between tenderness assessed by a panel and maximum shear force was -.50. The phenotypic correlation between those traits corrected for measurement errors was -.74. A correlation of zero was found between the total amount of collagen and meat tenderness, between amount of intramuscular fat and tenderness, and between ultimate pH and tenderness. The other correlations with meat tenderness ranged from -.00 for Minolta b* color coordinate to -.44 for drip loss. It was concluded that the measurement of maximum shear force can be used as an effective indicator of pig meat tenderness.

Animals↗