Effect of a personalized intensive dietary intervention on base excision repair (BER) in colorectal cancer patients: Results from a randomized controlled trial.

DNA repair is essential to maintain genomic integrity and may affect colorectal cancer (CRC) patients' risk of secondary cancers, treatment efficiency, and susceptibility to various comorbidities. Bioactive compounds identified in plant foods have the potential to modulate DNA repair mechanisms, but there is limited evidence of how dietary factors may affect DNA repair activity in CRC patients in remission after surgery. The aim of this study was to investigate the effect of a 6-month personalized intensive dietary intervention on DNA repair activity in post-surgery CRC patients (stage I-III). The present study included patients from the randomized controlled trial CRC-NORDIET, enrolled 2-9 months after surgery. The intervention group received an intensive dietary intervention emphasizing a prudent diet with specific plant-based foods suggested to dampen inflammation and oxidative stress, while the control group received only standard care advice. The comet-based in vitro repair assay was applied to assess DNA repair activity, specifically base excision repair (BER), in peripheral blood mononuclear cells (PBMCs). Statistical analyses were conducted using gamma generalized linear mixed models (Gamma GLMM). A total of 138 CRC patients were included, 72 from the intervention group and 66 from the control group. The BER activity in the intervention group did not change significantly compared to the control group. Our findings revealed a substantial range in both inter- and intra-individual levels of BER. In conclusion, the results do not support an effect of dietary intervention on BER activity in post-surgery CRC patients during a 6-month intervention period.

DNA base oxidation in relation to TNM stages and chemotherapy treatment in colorectal cancer patients 2-9 months post-surgery.

Accumulation of DNA damage is a critical feature of genomic instability, which is a hallmark of various cancers. The enzyme-modified comet assay is a recognized method to detect specific DNA lesions at the level of individual cells. In this cross-sectional investigation, we explore possible links between clinicopathological and treatment related factors, nutritional status, physical activity and function, and DNA damage in a cohort of colorectal cancer (CRC) patients with non-metastatic disease. Levels of DNA damage in peripheral mononuclear blood cells (PBMCs) assessed 2-9 months post-surgery, were compared across tumour stage (localized (stage I-II) vs. regional (stage III) disease), localization (colon vs. rectosigmoid/rectum cancer), and adjuvant chemotherapy usage, with the last dosage administrated 2-191 days prior to sampling. Associations between DNA damage and indicators of nutritional status, physical activity and function were also explored. In PBMCs, DNA base oxidation was higher in patients diagnosed with regional compared with localized tumours (P = 0.03), but no difference was seen for DNA strand breaks (P > 0.05). Number of days since last chemotherapy dosage was negatively associated with DNA base oxidation (P < 0.01), and patients recently receiving chemotherapy (<15 days before blood collection) had higher levels of DNA base oxidation than those not receiving chemotherapy (P = 0.03). In the chemotherapy group, higher fat mass (in kg and %) as well as lower physical activity were associated with greater DNA base oxidation (P < 0.05). In conclusion, DNA base oxidation measured with the enzyme-modified comet assay varies according to tumour and lifestyle related factors in CRC patients treated for non-metastatic disease.

Bilberry/red grape juice decreases plasma biomarkers of inflammation and tissue damage in aged men with subjective memory impairment -a randomized clinical trial.

BACKGROUND: Few randomized clinical trials have explored the health effects of bilberries in humans. The aim was to test the effect of bilberry and red grape-juice consumption on visual memory, motor speed and dexterity as well as inflammatory and tissue damage biomarkers of plasma in aged men with subjective memory impairment. METHODS: Nine-week double-blind, placebo-controlled, dietary intervention study of aged men (n = 60, age ≥ 67 years) with subjective memory impairment randomized to consume a 50/50 mix of bilberry/red grape-juice or an iso-caloric placebo juice. A selection of Cambridge Cognition Test Battery (CANTAB), Grooved Pegboard tests and blood-sampling for biomarker analysis were performed before and after the intervention. RESULTS: Compared to placebo the selected memory and motor test scores were un-affected by the bilberry/red grape intervention. However, the plasma levels of tissue damage biomarkers decreased significantly more in the bilberry/red grape group. In particular lactate dehydrogenase (LDH) decreased from 362 U/L (median, baseline) to 346 U/L (median, post intervention) in the bilberry/red grape group. Also, several biomarkers of inflammation (EGF, IL6, IL9, IL10 and TNFα) decreased significantly more in the bilberry/red grape group. Furthermore, several plasma polyphenols; p-coumaric acid, hippuric acid, protocatechuic acid, 3HPAA and vanillic acid, increased significantly more in the bilberry/red grape group compared to placebo with the largest increase in p-coumaric acid with 116%; from 2.2 [1.0,5.5] to 4.7 [2.8,8.1] µM/L (median [95% CL]). CONCLUSIONS: The results indicate that a nine-week bilberry/red grape juice intervention has no measurable effects on the selected memory scores in aged men experiencing memory problems but decreases the level of biomarkers of inflammation and tissue damage. Whether the dampening effects on inflammation and tissue damage biomarkers have relevance for neuroinflammatory brain pathology remains to be established. TRIAL REGISTRATION: Registration number ( ClinicalTrials.gov : NCT00972972 ), September 9, 2009.

Dietary Adjustments to Altitude Training in Elite Endurance Athletes; Impact of a Randomized Clinical Trial With Antioxidant-Rich Foods.

Background: Altitude training stresses several physiological and metabolic processes and alters the dietary needs of the athletes. International Olympic Committee (IOC)'s Nutrition Expert Group suggests that athletes should increase intake of energy, carbohydrate, iron, fluid, and antioxidant-rich foods while training at altitude. Objective: We investigated whether athletes adjust their dietary intake according to the IOC's altitude-specific dietary recommendations, and whether an in-between meal intervention with antioxidant-rich foods altered the athletes' dietary composition and nutrition-related blood parameters (mineral, vitamin, carotenoid, and hormone concentrations). Design: The dietary adjustments to altitude training (3 weeks at 2,320 m) were determined for 31 elite endurance athletes (23 ± 5 years, 23 males, 8 females) by six interviewer-administered 24-h dietary recalls on non-consecutive days; three before and during the altitude camp. The additional effect of in -between meal intervention with eucaloric antioxidant-rich or control snacks (1,000 kcal/day) was tested in a randomized controlled trial with parallel design. Results: At altitude the athletes increased their energy intake by 35% (1,430 ± 630 kcal/day, p < 0.001), the provided snacks accounting for 70% of this increase. Carbohydrate intake increased from 6.5 ± 1.8 g/kg body weight (BW) (50 E%) to 9.3 ± 2.1 g/kg BW (53 E%) (p < 0.001), with no difference between the antioxidant and control group. Dietary iron, fluid, and antioxidant-rich food intake increased by 37, 38, and 104%, respectively, in the whole cohort. The intervention group had larger increases in polyunsaturated fatty acids (PUFA), ω3 PUFA (n-3 fatty acids), ω6 PUFA (n-6 fatty acids), fiber, vitamin C, folic acid, and copper intake, while protein intake increased more among the controls, reflecting the nutritional content of the snacks. Changes in the measured blood minerals, vitamins, and hormones were not differentially affected by the intervention except for the carotenoid; zeaxanthin, which increased more in the intervention group (p < 0.001). Conclusions: Experienced elite endurance athletes increased their daily energy, carbohydrate, iron, fluid, and antioxidant-rich food intake during a 3-week training camp at moderate altitude meeting most of the altitude-specific dietary recommendations. The intervention with antioxidant-rich snacks improved the composition of the athletes' diets but had minimal impact on the measured nutrition-related blood parameters. Clinical Trial Registry Number: NCT03088891 (www.clinicaltrials.gov), Norwegian registry number: 626539 (https://rekportalen.no/).

Abnormal blood lactate accumulation during repeated exercise testing in myalgic encephalomyelitis/chronic fatigue syndrome.

Post-exertional malaise and delayed recovery are hallmark symptoms of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Studies on repeated cardiopulmonary exercise testing (CPET) show that previous exercise negatively affects oxygen uptake (VO2 ) and power output (PO) in ME/CFS. Whether this affects arterial lactate concentrations ([Laa ]) is unknown. We studied 18 female patients (18-50 years) fulfilling the Canadian Consensus Criteria for ME/CFS and 15 healthy females (18-50 years) who underwent repeated CPETs 24 h apart (CPET1 and CPET2 ) with [Laa ] measured every 30th second. VO2 at peak exercise (VO2peak ) was lower in patients than in controls on CPET1 (P < 0.001) and decreased in patients on CPET2 (P < 0.001). However, the difference in VO2peak between CPETs did not differ significantly between groups. [Laa ] per PO was higher in patients during both CPETs (Pinteraction  < 0.001), but increased in patients and decreased in controls from CPET1 to CPET2 (Pinteraction  < 0.001). Patients had lower VO2 (P = 0.02) and PO (P = 0.002) at the gas exchange threshold (GET, the point where CO2 production increases relative to VO2 ), but relative intensity (%VO2peak ) and [Laa ] at GET did not differ significantly from controls on CPET1 . Patients had a reduction in VO2 (P = 0.02) and PO (P = 0.01) at GET on CPET2 , but no significant differences in %VO2peak and [Laa ] at GET between CPETs. Controls had no significant differences in VO2 , PO or %VO2peak at GET between CPETs, but [Laa ] at GET was reduced on CPET2 (P = 0.008). In conclusion, previous exercise deteriorates physical performance and increases [Laa ] during exercise in patients with ME/CFS while it lowers [Laa ] in healthy subjects.

IRF4 Is a Critical Gene in Retinoic Acid-Mediated Plasma Cell Formation and Is Deregulated in Common Variable Immunodeficiency-Derived B Cells.

In the present study, we aimed at identifying the mechanisms whereby the vitamin A metabolite all-trans retinoic acid (RA) promotes the formation of plasma cells upon stimulation of B cells via the innate immunity receptors TLR9 and RP105. Most often, differentiation of B cells involves the sequential events of class switch recombination and somatic hypermutations characteristic of germinal center reactions, followed by plasma cell formation. By studying the regulatory networks known to drive these reactions, we revealed that RA enhances the expression of the plasma cell-generating transcription factors IFN regulatory factor (IRF)4 and Blimp1, and paradoxically also activation-induced deaminase (AID) involved in somatic hypermutations/class switch recombination, in primary human B cells. IRF4 was identified as a particularly important protein involved in the RA-mediated production of IgG in TLR9/RP105-stimulated B cells. Based on kinetic studies, we present a model suggesting that the initial induction of IRF4 by RA favors AID expression. According to this model, the higher level of IRF4 that eventually arises results in sustained elevated levels of Blimp1. Regarded as a master regulator of plasma cell development, Blimp1 will in turn suppress AID expression and drive the formation of IgG-secreting plasma cells. Notably, we demonstrated IRF4 to be deregulated in B cells from common variable immunodeficiency patients, contributing to the observed aberrant expression of AID in these patients. Taken together, the present study both provides new insight into the mechanisms whereby RA induces differentiation of B cells and identifies IRF4 as a key to understand the defective functions of B cells in common variable immunodeficiency patients.

The effect of kiwifruit consumption on blood pressure in subjects with moderately elevated blood pressure: a randomized, controlled study.

BACKGROUND AND AIMS: Kiwifruit contains bioactive substances that may lower blood pressure (BP) and improve endothelial function. We examined the effects of adding kiwifruit to the usual diet on 24-h ambulatory BP, office BP and endothelial function. METHODS: In a parallel-groups study, 118 subjects with high normal BP or stage 1 hypertension (systolic BP 130-159 mmHg and/or diastolic BP 85-99 mmHg) were randomized to intake of three kiwifruits (intervention) or one apple (control) a day for 8 weeks. Office and 24-h ambulatory BP was measured along with biomarkers of endothelial function including metabolites of nitric oxide (NO) formation and finger photo-plethysmography. RESULTS: At randomization, mean 24-h ambulatory systolic/diastolic BP was 133 ± 13/82 ± 9 mmHg (n = 106). After 8 weeks, BP was lower in the group assigned to kiwifruit versus apple intake (between group difference, - 3.6 mmHg [95% CI - 6.5 to - 0.7], p = 0.017 and - 1.9 mmHg [95% CI - 3.6 to - 0.3]; p = 0.040, for systolic and diastolic BP, respectively). Changes in office BP and endothelial function did not differ between the groups. CONCLUSIONS: Among men and women with moderately elevated BP, intake of three kiwifruits was associated with lower systolic and diastolic 24-h BP compared with one apple a day. The effect may be regulated by mechanisms other than improvement of endothelial function.

Effects of black tea on body composition and metabolic outcomes related to cardiovascular disease risk: a randomized controlled trial.

UNLABELLED: There is increasing evidence that tea and its non-caffeine components (primarily flavonoids) contribute to cardiovascular health. Randomized controlled trials have shown that tea can improve cardiovascular disease risk factors. We have previously reported a non-caffeine associated beneficial effect of regular black tea consumption on blood pressure and its variation. OBJECTIVE: To explore the non-caffeine associated effects of black tea on body weight and body fat distribution, and cardiovascular disease related metabolic outcomes. DESIGN: regular tea-drinking men and women (n = 111; BMI 20-35 kg m(-2)) were recruited to a randomized controlled double-blind 6 month parallel-designed trial. Participants consumed 3 cups per day of either powdered black tea solids (tea) or a flavonoid-free flavour- and caffeine-matched placebo (control). Body weight, waist- and hip-circumference, endothelial function and plasma biomarkers were assessed at baseline, 3 months and 6 months. RESULTS: Compared to control, regular ingestion of black tea over 3 months inhibited weight gain (-0.64 kg, p = 0.047) and reduced waist circumference (-1.88 cm, P = 0.035) and waist-to-hip ratio (-0.03, P = 0.005). These effects were no longer significant at 6 months. There were no significant effects observed on fasting glucose, insulin, plasma lipids or endothelial function. CONCLUSION: Our study suggests that short-term regular ingestion of black tea over 3 months can improve body weight and body fat distribution, compared to a caffeine-matched control beverage. However, there was no evidence that these effects were sustained beyond 3 months.

Stress associated gene expression in blood cells is related to outcome in radiotherapy treated head and neck cancer patients.

BACKGROUND: We previously observed that a radiotherapy-induced biochemical response in plasma was associated with favourable outcome in head and neck squamous carcinoma cancer (HNSCC) patients. The aim of the present study was to compare stress associated blood cell gene expression between two sub-groups of HNSCC patients with different biochemical responses to radiotherapy. METHODS: Out of 87 patients (histologically verified), 10 biochemical 'responders' having a high relative increase in plasma oxidative damage and a concomitant decrease in plasma antioxidants during radiotherapy and 10 'poor-responders' were selected for gene-expression analysis and compared using gene set enrichment analysis. RESULTS: There was a significant induction of stress-relevant gene-sets in the responders following radiotherapy compared to the poor-responders. The relevance of the involvement of similar stress associated gene expression for HNSCC cancer and radioresistance was verified using two publicly available data sets of 42 HNSCC cases and 14 controls (GEO GSE6791), and radiation resistant and radiation sensitive HNSCC xenografts (E-GEOD-9716). CONCLUSIONS: Radiotherapy induces a systemic stress response, as revealed by induction of stress relevant gene expression in blood cells, which is associated to favourable outcome in a cohort of 87 HNSCC patients. Whether these changes in gene expression reflects a systemic effect or are biomarkers of the tumour micro-environmental status needs further study. TRIAL REGISTRATION: Raw data are available at ArrayExpress under accession number E-MEXP-2460.

Effects of tea and coffee on cardiovascular disease risk.

Tea and coffee have been associated with risk of cardiovascular disease (CVD), both positively and negatively. Epidemiological data suggest that black and green tea may reduce the risk of both coronary heart disease and stroke by between 10 and 20%. Experimental and clinical trial data generally indicate either neutral or beneficial effects on risk factors and pathways linked to the development of CVD. Controversy still exists regarding the effects of coffee, where there have been concerns regarding associations with hypercholesterolaemia, hypertension and myocardial infarction. However, long term moderate intake of coffee is not associated with detrimental effects in healthy individuals and may even protect against the risk of developing type 2 diabetes. The detrimental effects of coffee may be associated with the acute pressor effects, most likely due to caffeine at high daily intakes, and lipids from boiled coffee can contribute to raised serum cholesterol. Genetic polymorphisms in enzymes involved in uptake, metabolism and excretion of tea and coffee compounds are also associated with differential biological effects. Potential mechanisms by which tea and coffee phytochemicals can exert effects for CVD protection include the regulation of vascular tone through effects on endothelial function, improved glucose metabolism, increased reverse cholesterol transport and inhibition of foam cell formation, inhibition of oxidative stress, immunomodulation and effects on platelet function (adhesion and activation, aggregation and clotting). The phytochemical compounds in tea and coffee and their metabolites are suggested to influence protective endogenous pathways by modulation of gene-expression. It is not known exactly which compounds are responsible for the suggestive protective effects of tea and coffee. Although many biologically active compounds have been identified with known biological effects, tea and coffee contain many unidentified compounds with potential bioactivity.

Blood cell gene expression associated with cellular stress defense is modulated by antioxidant-rich food in a randomised controlled clinical trial of male smokers.

BACKGROUND: Plant-based diets rich in fruit and vegetables can prevent development of several chronic age-related diseases. However, the mechanisms behind this protective effect are not elucidated. We have tested the hypothesis that intake of antioxidant-rich foods can affect groups of genes associated with cellular stress defence in human blood cells. TRIAL REGISTRATION NUMBER: NCT00520819 http://clinicaltrials.gov. METHODS: In an 8-week dietary intervention study, 102 healthy male smokers were randomised to either a diet rich in various antioxidant-rich foods, a kiwifruit diet (three kiwifruits/d added to the regular diet) or a control group. Blood cell gene expression profiles were obtained from 10 randomly selected individuals of each group. Diet-induced changes on gene expression were compared to controls using a novel application of the gene set enrichment analysis (GSEA) on transcription profiles obtained using Affymetrix HG-U133-Plus 2.0 whole genome arrays. RESULTS: Changes were observed in the blood cell gene expression profiles in both intervention groups when compared to the control group. Groups of genes involved in regulation of cellular stress defence, such as DNA repair, apoptosis and hypoxia, were significantly upregulated (GSEA, FDR q-values < 5%) by both diets compared to the control group. Genes with common regulatory motifs for aryl hydrocarbon receptor (AhR) and AhR nuclear translocator (AhR/ARNT) were upregulated by both interventions (FDR q-values < 5%). Plasma antioxidant biomarkers (polyphenols/carotenoids) increased in both groups. CONCLUSIONS: The observed changes in the blood cell gene expression profiles suggest that the beneficial effects of a plant-based diet on human health may be mediated through optimization of defence processes.

Bilberry juice modulates plasma concentration of NF-kappaB related inflammatory markers in subjects at increased risk of CVD.

PURPOSE: Bilberries are abundant in polyphenols. Dietary polyphenols have been associated with strategies for prevention and treatment of chronic inflammatory diseases. We investigated the effect of bilberry juice on serum and plasma biomarkers of inflammation and antioxidant status in subjects with elevated levels of at least one risk factor for cardiovascular disease (CVD). METHODS: In a randomized controlled trial, participants consumed either bilberry juice (n = 31) or water (n = 31) for 4 weeks. RESULTS: Supplementation with bilberry juice resulted in significant decreases in plasma concentrations of C-reactive protein (CRP), interleukin (IL)-6, IL-15, and monokine induced by INF-gamma (MIG). Unexpectedly, an increase in the plasma concentration of tumor nuclear factor-alpha (TNF-alpha) was observed in the bilberry group. CRP, IL-6, IL15, MIG, and TNF-alpha are all target genes of nuclear factor- kappa B (NF-kappaB), -a transcription factor that is crucial in orchestrating inflammatory responses. Plasma quercetin and p-coumaric acid increased in the bilberry group, otherwise no differences were observed for clinical parameters, oxidative stress or antioxidant status. Furthermore, we studied the effect of polyphenols from bilberries on lipopolysaccharide (LPS)-induced NF-kappaB activation in a monocytic cell line. We observed that quercetin, epicatechin, and resveratrol inhibited NF-kappaB activation. CONCLUSIONS: These findings suggest that supplementation with bilberry polyphenols may modulate the inflammation processes. Further testing of bilberry supplementation as a potential strategy in prevention and treatment of chronic inflammatory diseases is warranted.

The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide.

BACKGROUND: A plant-based diet protects against chronic oxidative stress-related diseases. Dietary plants contain variable chemical families and amounts of antioxidants. It has been hypothesized that plant antioxidants may contribute to the beneficial health effects of dietary plants. Our objective was to develop a comprehensive food database consisting of the total antioxidant content of typical foods as well as other dietary items such as traditional medicine plants, herbs and spices and dietary supplements. This database is intended for use in a wide range of nutritional research, from in vitro and cell and animal studies, to clinical trials and nutritional epidemiological studies. METHODS: We procured samples from countries worldwide and assayed the samples for their total antioxidant content using a modified version of the FRAP assay. Results and sample information (such as country of origin, product and/or brand name) were registered for each individual food sample and constitute the Antioxidant Food Table. RESULTS: The results demonstrate that there are several thousand-fold differences in antioxidant content of foods. Spices, herbs and supplements include the most antioxidant rich products in our study, some exceptionally high. Berries, fruits, nuts, chocolate, vegetables and products thereof constitute common foods and beverages with high antioxidant values. CONCLUSIONS: This database is to our best knowledge the most comprehensive Antioxidant Food Database published and it shows that plant-based foods introduce significantly more antioxidants into human diet than non-plant foods. Because of the large variations observed between otherwise comparable food samples the study emphasizes the importance of using a comprehensive database combined with a detailed system for food registration in clinical and epidemiological studies. The present antioxidant database is therefore an essential research tool to further elucidate the potential health effects of phytochemical antioxidants in diet.

Content of redox-active compounds (ie, antioxidants) in foods consumed in the United States.

BACKGROUND: Supplements containing ascorbic acid, alpha-tocopherol, or beta-carotene do not protect against oxidative stress-related diseases in most randomized intervention trials. We suggest that other redox-active phytochemicals may be more effective and that a combination of different redox-active compounds (ie, antioxidants or reductants) may be needed for proper protection against oxidative damage. OBJECTIVE: We aimed to generate a ranked food table with values for total content of redox-active compounds to test this alternative antioxidant hypothesis. DESIGN: An assay that measures the total concentration of redox-active compounds above a certain cutoff reduction potential was used to analyze 1113 food samples obtained from the US Department of Agriculture National Food and Nutrient Analysis Program. RESULTS: Large variations in the content of antioxidants were observed in different foods and food categories. The food groups spices and herbs, nuts and seeds, berries, and fruit and vegetables all contained foods with very high antioxidant contents. Most food categories also contained products almost devoid of antioxidants. Of the 50 food products highest in antioxidant concentrations, 13 were spices, 8 were in the fruit and vegetables category, 5 were berries, 5 were chocolate-based, 5 were breakfast cereals, and 4 were nuts or seeds. On the basis of typical serving sizes, blackberries, walnuts, strawberries, artichokes, cranberries, brewed coffee, raspberries, pecans, blueberries, ground cloves, grape juice, and unsweetened baking chocolate were at the top of the ranked list. CONCLUSION: This ranked antioxidant food table provides a useful tool for investigations into the possible health benefit of dietary antioxidants.

Water-miscible, emulsified, and solid forms of retinol supplements are more toxic than oil-based preparations.

BACKGROUND: It is well established that an excessive intake of retinol (vitamin A) is toxic; however, it has been > 25 y since the last extensive treatise of case reports on this subject. OBJECTIVE: The objectives were to identify and evaluate all individual cases of retinol toxicity published in the scientific literature that assessed the thresholds and symptoms induced by high intakes of retinol and to compare the toxicity of different physical forms of retinol preparations. DESIGN: We performed a meta-analysis of case reports on toxicity claimed to be induced by intakes of excessive amounts of dietary retinol (ie, retinol and retinyl esters in foods or supplements). Using free text and MESH (medical subheading) strategies in PubMed, we identified 248 articles in the scientific literature. From these initial articles we identified other relevant citations. The final database consisted of 259 cases in which individual data on dose, sex, age, time of exposure, and symptoms are reported. RESULTS: Chronic hypervitaminosis A is induced after daily doses of 2 mg retinol/kg in oil-based preparations for many months or years. In contrast, doses as low as 0.2 mg retinol. kg(-1). d(-1) in water-miscible, emulsified, and solid preparations for only a few weeks caused chronic hypervitaminosis A. Thus, water-miscible, emulsified, and solid preparations of retinol are approximately 10 times as toxic as are oil-based retinol preparations. The safe upper single dose of retinol in oil or liver seems to be approximately 4-6 mg/kg body wt. These thresholds do not vary considerably with age. CONCLUSIONS: The results of the present study indicate that the physical form of retinol supplements is a major determinant of toxicity. The use of water-miscible, emulsified, and solid preparations of retinol should therefore be carefully considered before being used in supplements and fortifications.