Vitamin A hepatotoxicity: a cautionary note regarding 25,000 IU supplements

Vitamin A-containing dietary supplements from German and US online pharmacies: market and risk assessment

Vitamin A supplements are used by many people, and the number of newly registered dietary supplements is continuously increasing. The preparations fall under food law and are not subject to the strict controls of pharmaceuticals. Risk indications and maximum quantity recommendations, e.g., from the Bundesinstitut für Risikobewertung (BfR) and the U.S. Food and Drug Administration (FDA) are not binding, which means that overdoses and potentially serious health problems can easily occur. The hepatotoxicity and teratogenicity of vitamin A are well documented, and other negative effects of high doses of vitamin A are also being discussed. Nevertheless, preparations with exorbitantly high doses are freely available for sale and unrestricted. In this study, 75 supplements containing vitamin A available in Germany and 26 available in the USA were critically examined on the basis of various parameters such as the recommended daily dose according to the manufacturer, daily therapy costs (DTC), the presence of warnings about overdose, use during pregnancy and breastfeeding, and information on adverse effects/interactions. The aim was to gain insights into their risk potential and to examine the need for closer monitoring and stricter guidelines for these preparations. The results show some considerable country-specific differences. Overall, there are serious deficiencies in compliance with the labeling requirements for both the German and the US preparations, and the dosages are often far too high in view of the applicable expert recommendations. Overall, these deficits can pose a risk for consumers that is difficult to assess in its entirety, especially for vulnerable consumer groups. It should be noted that the US preparations perform better overall than the German preparations. This suggests better regulation of dietary supplements in the US market. Based on the available data and literature research, it is doubtful whether the intake of vitamin A-containing preparations, without a diagnosed vitamin A deficiency, has a positive health benefit. Furthermore, it should be examined whether vitamin A should continue to be offered over-the-counter as a food supplement.

Scientific opinion on the tolerable upper intake level for preformed vitamin A and β-carotene

Following two requests from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver a scientific opinion on the revision of the tolerable upper intake level (UL) for preformed vitamin A and β-carotene. Systematic reviews of the literature were conducted for priority adverse health effects of excess vitamin A intake, namely teratogenicity, hepatotoxicity and endpoints related to bone health. Available data did not allow to address whether β-carotene could potentiate preformed vitamin A toxicity. Teratogenicity was selected as the critical effect on which to base the UL for preformed vitamin A. The Panel proposes to retain the UL for preformed vitamin A of 3000 μg RE/day for adults. This UL applies to men and women, including women of child-bearing age, pregnant and lactating women and post-menopausal women. This value was scaled down to other population groups using allometric scaling (body weight0.75), leading to ULs between 600 μg RE/day (infants 4-11 months) and 2600 μg RE/day (adolescents 15-17 years). Based on available intake data, European populations are unlikely to exceed the UL for preformed vitamin A if consumption of liver, offal and products thereof is limited to once per month or less. Women who are planning to become pregnant or who are pregnant are advised not to consume liver products. Lung cancer risk was selected as the critical effect of excess supplemental β-carotene. The available data were not sufficient and suitable to characterise a dose-response relationship and identify a reference point; therefore, no UL could be established. There is no indication that β-carotene intake from the background diet is associated with adverse health effects. Smokers should avoid consuming food supplements containing β-carotene. The use of supplemental β-carotene by the general population should be limited to the purpose of meeting vitamin A requirements.

Liver toxicity from vitamin A

Hepatic toxicity secondary to hypervitaminosis A is extremely rare. We report the case of a 27‐year‐old Caucasian female who presented for an investigation of abdominal pain, cholestatic liver function tests, and abnormal computerized tomography findings. She had been prescribed isotretinoin for her acne and had subsequently purchased vitamin A online, which she consumed daily for over 18 months.

The Prevalence of Dietary Supplement Use Among Elementary, Junior High, and High School Students: A Nationwide Survey in Japan

The prevalence of dietary supplement use, such as vitamins, minerals, or fish oil, has increased among children in Japan; however, whether children are using dietary supplements appropriately remains unclear. This study aimed to determine dietary supplement use among children. In August 2017, a nationwide internet preliminary survey of 265,629 mothers aged from 25 to 59 years old was undertaken. Of these, 19,041 mothers of children attending either elementary school, junior high school, or high school were selected. Among them, 16.4% were currently providing their children with dietary supplements and 5.2% had previously given dietary supplements to their children. The prevalence of dietary supplement use was higher in boys than in girls, and the prevalence increased according to their grade. A total of 2439 participants were eligible to undertake a targeted survey on dietary supplement use. Dietary supplements were being taken to maintain health, supplement nutrients, and enhance growth in both boys and girls, and many children (37.5%) were provided with vitamin and mineral supplements. Mothers mainly obtained information concerning dietary supplements via the internet, and supplements were purchased in drug stores or via the internet. The prevalence of dietary supplement use in mothers was 65.4% and may be associated with the prevalence rates in children. Some mothers reported adverse events (3.6%) in their children, such as stomachache, diarrhea, nausea and vomiting, and constipation. The cause-and-effect relationships for adverse events were not clear, but some children were given products for adults. Children are more influenced by dietary supplements compared to adults. To prevent adverse events due to inappropriate use, parental education concerning dietary supplements is essential.

Liver toxicity related to herbs and dietary supplements: Online table of case reports. Part 2 of 5 series

BACKGROUND

No online current list of potentially life-threatening, hepatotoxic herbs and dietary supplements based on PubMed case reports exists in a summarized tabular form.

METHODS

Documented case reports of herbs or dietary supplements (DS; includes herbs) appearing to contribute to liver injury were used to create an online "DS Toxic Table" of potentially hepatotoxic herbs and dietary supplements (PubMed, 1966 to June, 2016, and cross-referencing). The spectrum of DS induced liver injuries (DSILI) included elevated liver enzymes, hepatitis, steatosis, cholestasis, hepatic necrosis, hepatic fibrosis, hepatic cirrhosis, veno-occlusive disease, acute liver failure requiring a liver transplant, and death.

RESULTS

Over the past 50 years, approximately 21 herbs (minus germander and usnic acid that are no longer sold) and 12 dietary supplements (minus the nine no longer sold and vitamin A & niacin due to excess intake) posed a possible risk for liver injures in certain individuals. The herbs with the most number of reported publications (but not cases studies) in descending order, were germander, black cohosh, kava extract, and green tea extract.

CONCLUSION

These online DS Toxic Tables will contribute to continued Phase IV post marketing surveillance to detect possible liver toxicity cases and serve to forewarn consumers, clinicians, and corporations.

Hepatotoxicity by Dietary Supplements: A Tabular Listing and Clinical Characteristics

Dietary supplements (DS) are extensively consumed worldwide despite unproven efficacy. The true incidence of DS-induced liver injury (DSILI) is unknown but is probably under-diagnosed due to the general belief of safety of these products. Reported cases of herbals and DS-induced liver injury are increasing worldwide. The aim of this manuscript is to report a tabular listing with a description of DS associated with hepatotoxicity as well as review the phenotype and severity of DSILI. Natural remedies related to hepatotoxicity can be divided into herbal product-induced liver injury and DS-induced liver injury. In this article, we describe different DS associated with liver injury, some of them manufactured DS containing several ingredients (Herbalife™ products, Hydroxycut™, LipoKinetix™, UCP-1 and OxyELITE™) while others have a single ingredient (green tea extract, linoleic acid, usnic acid, 1,3-Dimethylamylamine, vitamin A, Garcinia cambogia and ma huang). Additional DS containing some of the aforementioned ingredients implicated in liver injury are also covered. We have also included illicit androgenic anabolic steroids for bodybuilding in this work, as they are frequently sold under the denomination of DS despite being conventional drugs.

Liver abnormalities in drug and substance abusers

Drug and substance abuse remains a major medical problem. Alcohol use, abuse and dependence are highly prevalent conditions. Alcohol related liver disease can present as simple steatosis, steatohepatitis, alcoholic hepatitis or liver cirrhosis. Paracetamol hepatotoxicity secondary to accidental or deliberate overdose is another common problem. While the adverse cardiovascular, neurological, renal and psychiatric consequences of various illicit substance abuses are widely studied and publicized, less attention has been directed towards possible hepatotoxic effects. Illicit drug abuse can cause a range of liver abnormalities ranging from asymptomatic derangement of liver function tests to fulminant hepatic failure. This article reviews the epidemiology, risk factors, clinical manifestations, pathogenesis, investigations, management and prognostic factors of alcohol related liver disease and paracetamol hepatotoxicity as well as the current knowledge pertaining to hepatotoxicity of the more commonly used illicit substances including cannabis, amphetamine type stimulants, cocaine, khat chewing and complementary and alternate medicine.

Review of liver injury associated with dietary supplements

Dietary supplements (DS) are easily available and increasingly used, and adverse hepatic reactions have been reported following their intake. To critically review the literature on liver injury because of DSs, delineating patterns and mechanisms of injury and to increase the awareness towards this cause of acute and chronic liver damage. Studies and case reports on liver injury specifically because of DSs published between 1990 and 2010 were searched in the PubMed and EMBASE data bases using the terms 'dietary/nutritional supplements', 'adverse hepatic reactions', 'liver injury'; 'hepatitis', 'liver failure', 'vitamin A' and 'retinoids', and reviewed for yet unidentified publications. Significant liver injury was reported after intake of Herbalife and Hydroxycut products, tea extracts from Camellia sinensis, products containing usnic acid and high contents of vitamin A, anabolic steroids and others. No uniform pattern of hepatotoxicity has been identified and severity may range from asymptomatic elevations of serum liver enzymes to hepatic failure and death. Exact estimates on how frequent adverse hepatic reactions occur as a result of DSs cannot be provided. Liver injury from DSs mimicking other liver diseases is increasingly recognized. Measures to reduce risk include tighter regulation of their production and distribution and increased awareness of users and professionals of the potential risks.

All-trans retinoic acid alleviates hepatic ischemia/reperfusion injury by enhancing manganese superoxide dismutase in rats

All-trans retinoic acid (atRA) is an active metabolite of vitamin A with antioxidant effects. There have been few reports on the effects of atRA on liver ischemia/reperfusion (I/R) injury. Here we have used a rat liver ischemia/ reperfusion model to analyze the protective effect of atRA. Rats were administered with different does (5-15 mg/kg/d) of atRA intraperitoneally (i.p.) for 14 d before I/R. Partial (70%) hepatic ischemia was induced by clamping the hepatic artery, portal vein, and bile duct to the left and median lobes of the liver using a vascular clamp for 60 min, followed by 24 h of reperfusion. The serum aminotransferase (ALT and AST) and hepatic pathology were used to evaluate I/R injury. The results demonstrate that atRA pretreatment attenuates liver I/R injury by inhibiting the release of malondialdehyde (MDA) and by enhancing the activity of superoxide dismutase (SOD). To gain insight into the mechanism of the SOD up-regulation by atRA, the activity of p38 mitogenactivated protein kinase (p38MAKP) and Akt was measured. The results showed that the phosphorylation of p38MAPK and Akt paralleled the expression of manganese superoxide dismutase (MnSOD). That these activities are related was demonstrated by the addition of a p38 inhibitor which markedly decreased MnSOD levels. Taken together, our data reveal that atRA can protect liver from I/R injury by increaseing MnSOD, which is associated with an increased activity of p38MAPK and Akt.

The elderly as a sensitive population in environmental exposures: making the case

The US population is aging. CDC has estimated that 20% of all Americans will be 65 or older by the year 2030. As a part of the aging process, the body gradually deteriorates and physiologic and metabolic limitations arise. Changes that occur in organ anatomy and function present challenges for dealing with environmental stressors of all kinds, ranging from temperature regulation to drug metabolism and excretion. The elderly are not just older adults, but rather are individuals with unique challenges and different medical needs than younger adults. The ability of the body to respond to physiological challenge presented by environmental chemicals is dependent upon the health of the organ systems that eliminate those substances from the body. Any compromise in the function of those organ systems may result in a decrease in the body's ability to protect itself from the adverse effects of xenobiotics. To investigate this issue, we performed an organ system-by-organ system review of the effects of human aging and the implications for such aging on susceptibility to drugs and xenobiotics. Birnbaum (1991) reported almost 20 years ago that it was clear that the pharmacokinetic behavior of environmental chemicals is, in many cases, altered during aging. Yet, to date, there is a paucity of data regarding recorded effects of environmental chemicals on elderly individuals. As a result, we have to rely on what is known about the effects of aging and the existing data regarding the metabolism, excretion, and adverse effects of prescription medications in that population to determine whether the elderly might be at greater risk when exposed to environmental substances. With increasing life expectancy, more and more people will confront the problems associated with advancing years. Moreover, although proper diet and exercise may lessen the immediate severity of some aspects of aging, the process will continue to gradually degrade the ability to cope with a variety of injuries and diseases. Thus, the adverse effects of long-term, low-level exposure to environmental substances will have a longer time to be manifested in a physiologically weakened elderly population. When such exposures are coupled with concurrent exposure to prescription medications, the effects could be devastating. Public health officials must be knowledgeable about the sensitivity of the growing elderly population, and ensure that the use of health guidance values (HGVs) for environmental contaminants and other substances give consideration to this physiologically compromised segment of the population.

[Pathology along the liver sinusoids: endothelial and perisinusoidal findings]

Sinusoidal alterations unrelated to primary hepatocellular damage present without characteristic clinical findings and in these cases the liver biopsy is particularly important. Capillarization of sinusoids is characterized by closing of fenestration, formation of a basal membrane and by the expression of CD34 and is typical for active cirrhosis. In nodular regeneratory hyperplasia, capillarization indicates a local or general disturbance of perfusion. In large regenerative nodules, focal nodular hyperplasia and liver cell adenoma CD34-positive capillaries reflect afferent parts and CD34-negative sinusoids the efferent parts of the parenchymal vascular bed. HCC generally have a completely capillarized CD34-positive vascular bed. Hepatic angiosarcomas and epithelioid hemangioendotheliomas can be easily overseen in liver biopsies, if they spread along the sinusoids without detoriation of the acinar architecture and without significant alteration of the surrounding liver cell plates. Toxic damage of endothelial cells, post-sinusoidal stasis and sinusoidal hyperperfusion are the underlying pathogenetic principles of sinusoidal injury. Rupture and loss of the perisinusoidal reticulin fibres lead to peliosis hepatis. In these cases liver biopsy might disclose occlusion of the terminal liver veins (VOD). Perisinusoidal fibrosis can be caused by intrasinusoidal accumulation of pathologic cells, advanced intrasinusoidal macrophagocytic storage diseases and by activation of the vitamin A-storing hepatic stellate cells. Perisinusoidal amyloidosis can be the first sign of an underlying B-cell neoplasia.

Vitamin A toxicosis in a lorikeet flock

Vitamin A toxicosis has recently been recognized as a concern for granivorous birds such as cockatiels (Nymphicus hollandicus) and nectarivorous birds such as lorikeets. Such birds have little exposure to performed vitamin A in their wild diet, relying on carotene conversion to supply their vitamin A needs. Multiple clinical problems arose in a lorikeet flock when excessive vitamin A supplementation was used.

Risk of vitamin A toxicity from candy-like chewable vitamin supplements for children

Numerous vitamin supplements are available over-the-counter to the general public. Some such supplements are available as candy-like chewable preparations to encourage consumption by children. We report 3 cases of overdose of such preparations. Each patient had taken an estimated 200,000 to 300,000 IU of vitamin A. Their circulating vitamin A (retinol and retinyl palmitate) concentrations were monitored over a 6-month period. There were no clinical or biochemical complications noted. However, there were marked increases in both retinol and retinyl palmitate concentrations above age-related reference ranges. In particular, it took 1 to 3 weeks for the serum retinol concentrations to peak and many months for them to normalize. Parents should be warned about the dangers of excessive vitamin consumption. Clinicians should be aware of the late peak in serum retinol concentrations, which may lead to late complications of vitamin A overdose.

Growth arrest and decrease of alpha-SMA and type I collagen expression by palmitic acid in the rat hepatic stellate cell line PAV-1

Liver fibrosis is characterized by an activation of hepatic stellate cells (HSC). During primary culture HSC evolve from a quiescent into an activated phenotype which is characterized by alpha-smooth muscle actin (alpha-SMA) up-regulation, increase in cell growth, and extracellular matrix secretion. HSC culture with trans-resveratrol can lead to deactivation of myofibroblast-like HSC. We used an HSC line, PAV-1, to check the role of retinol and palmitic acid in the deactivation process of HSC. Using mass and metabolic-based methods, Western blot and immunocytochemistry assays, we demonstrated that treatment with palmitic acid (75 muM) alone or in combination with retinol (2 muM) significantly decreased cell proliferation and alpha-SMA expression. We also established that the association of both compounds strongly decreased collagen type I expression. Our results suggest the potential use of palmitic acid alone or in combination with retinol to induce HSC deactivation.

Drug-induced hepatotoxicity: 2005

The removal from the marketplace of several widely prescribed drugs due to hepatotoxicity has attracted considerable attention. Now under extensive review are means by which we can better identify hepatic risk prior to federal approval. Assessment of risk-to-benefit ratios regarding a novel agent with hepatotoxicity issues (especially one for a life-threatening condition) requires considerable judgment and education on the part of prescribers and patients. The spectrum of drug-induced liver injury is broad with simulation of almost all unknown liver disorders. Drug-induced liver injuries often have a somewhat characteristic signature, as regards type of injury (hepatocellular vs cholestatic) and time of onset. The diagnosis of drug-induced liver injury is often one of exclusion with initial suspicion based on circumstantial evidence. Factors affecting susceptibility to drug-induced injury include age, sex, concomitant use of other drugs, and genetic polymorphism in metabolic pathways involved in activation or disposition of therapeutic drugs. Drug-drug interactions present particular problems in patients, often elderly, who are receiving several drugs simultaneously. Mechanisms of drug-induced liver injury are many and varied. With many drugs, intermediary products produced during metabolism are highly reactive and toxic. In these situations, the balance between the rate of production of the metabolite and the effectiveness of the drug may determine whether or not hepatic injury occurs.

Nutraceuticals--a pharmaceutical viewpoint: part II

PURPOSE OF REVIEW

To review pharmaceutical and pharmacological issues relating to the benefits and risks associated with the use of naturally sourced nutraceuticals when administered singly or in combinations.

RECENT FINDINGS

The application of vegetable extracts or dietary supplementation with selenium or antioxidant vitamins results in positive benefits on immunity and other phenomena associated with chronic diseases, ageing and cancer. However, there appear to be no cardiovascular benefits from vitamin mixtures, which may in fact cause harm. Therefore, although recent publications have increased our understanding of the metabolic actions of nutraceuticals, learning to use them to the best advantage is going to require products with uniform and consistent quality. Unfortunately, a single purified substance will not always have the same antioxidant activity, nor provide the same clinical benefits as nutraceutical mixtures and combinations occurring in natural extracts. In order to perform first-class clinical studies to determine safety and efficacy, the stability, compatibility and other pharmaceutical variables inherent in many of these combination products will have to be better controlled.

SUMMARY

Nutraceuticals have potent biological actions. Their use is increasing dramatically, and there is growing evidence of clinical benefits. No medicinal products are completely safe so their risks need to be characterized and controlled. Imposing pharmaceutical levels of control and regulation would increase costs and reduce patient access to new products, but the evidence is compelling that closer monitoring of raw materials, processing and formulation will be required to maximize the benefits and minimize the risks.

Adverse reaction to a dietary supplement in an elderly patient

OBJECTIVE

To describe the case of an elderly patient who experienced hepatic enzyme elevations and symptoms of hepatitis associated with the administration of a dietary supplement.

CASE SUMMARY

A 92-year-old white woman with no history of hepatic disease developed jaundice and increased confusion associated with increased hepatic enzymes. The hepatitis panel, abdominal ultrasound, and antinuclear antibody screen indicated no abnormalities. A drug regimen review revealed that the patient was receiving a dietary supplement, Nutrilite Double X Multivitamin-Multimineral. Following discontinuation of the supplement, the patient's symptoms resolved and the hepatic enzymes decreased or returned to the reference range at evaluations occurring 1 week and 1 month after intervention. An objective causality assessment revealed this to be a probable adverse drug event.

DISCUSSION

While the association of certain herbal preparations with hepatotoxicity has been demonstrated, the potential for this adverse effect is easily overlooked. In this patient, infectious or autoimmune causes of acute hepatitis were ruled out, and drug-induced causes were considered. The resolution of symptoms and laboratory values following discontinuation of the supplement support a relationship between the dietary supplement and this episode of hepatitis.

CONCLUSIONS

Our case indicates that there was a probable relationship between the dietary supplement Nutrilite Double X Multivitamin-Multimineral and the development of acute hepatitis. Due to the multi-ingredient formulation of the product, as well as lack of data describing manufacturing procedures, it is difficult to determine which component may be associated with this effect. Over-the-counter supplements should be considered as a part of the differential diagnosis in patients presenting with increased liver enzymes and related symptoms.

Estimating the potential for vitamin A toxicity in women and young children

This paper describes usual intakes of vitamin A from diet plus low dose supplements, reviews methods for assessing vitamin A toxicity and applies a kinetic analysis of vitamin A turnover to estimate the effect of high dose supplements on vitamin A liver stores in infants and young children. In the United States, the 95th percentile of intake by preschoolers from foods and supplements exceeds the tolerable upper level (UL) but is below the no-observed-adverse-effect level (NOAEL). The 95th percentile of vitamin A intake from foods and supplements for nonpregnant, nonlactating women aged 19-30 y also exceeds the UL but is below the NOAEL for women of reproductive age. In low income populations in developing countries, vitamin A intakes of preschoolers and women consuming foods plus low dose supplements can also exceed the UL but are unlikely to exceed the NOAEL. There are few data on which to establish thresholds for excessive vitamin A intake or vitamin A concentrations in tissues. To assess the potential toxicity of the new recommendations (see article by Ross in this issue) for high dose vitamin A supplements for infants and children, we used a kinetic approach to estimate accumulation of the vitamin in liver. The new recommendations are unlikely to result in toxic levels (>300 microg per gram of liver) even if high dose supplements are inadvertently given monthly. The kinetic analysis also illustrates that a constant supply of vitamin A from breast milk (and/or complementary foods) is vital for preventing depletion of liver vitamin A stores between high dose supplements.

Serum retinyl esters are not associated with biochemical markers of liver dysfunction in adult participants in the third National Health and Nutrition Examination Survey (NHANES III), 1988--1994

BACKGROUND

Serum retinyl ester concentrations are elevated in hypervitaminosis A. It was suggested that retinyl esters >10% of total serum vitamin A indicate potential hypervitaminosis, but this cutoff was derived from small clinical samples that may not be representative of the general population.

OBJECTIVE

We sought to examine the distribution of serum retinyl ester concentrations and associations between retinyl ester concentrations and biochemical markers of liver dysfunction in a nationally representative sample.

DESIGN

We assessed the associations between serum retinyl ester concentrations and 5 biochemical indexes of liver dysfunction by using multivariate linear and multiple logistic regression techniques and controlling for age, sex, use of supplements containing vitamin A, alcohol consumption, smoking status, and use of exogenous estrogens in 6547 adults aged > or =18 y in the third National Health and Nutrition Examination Survey (NHANES III), 1988--1994.

RESULTS

Thirty-seven percent of the sample had serum retinyl ester concentrations >10% of total serum vitamin A and 10% of the sample had serum retinyl esters >15% of total vitamin A. We found no associations between serum retinyl ester concentrations and 1) concentrations of any biochemical variable (multiple linear regression) or 2) risk of having biochemical variables above the reference range (multiple logistic regression). We did not find a serum retinyl ester value with statistically significant sensitivity and specificity for predicting increases in biochemical indexes of liver dysfunction.

CONCLUSIONS

The prevalence of serum retinyl ester concentrations >10% of the total vitamin A concentration in the NHANES III sample was substantially higher than expected but elevated retinyl ester concentrations were not associated with abnormal liver function.

Herbal and alternative medicine

An extensive range of herbal and dietary supplements is now available, and use of these products by ED patients is fairly common. Emergency physicians should be familiar with some of the products used more frequently for common complaints. Emergency personnel also should be vigilant for toxic syndromes resulting from ingestion of certain of these products and be wary of possible toxicity from any of these supplements owing to their minimal quality control and absence of FDA regulation.

Regulation of hepatic vitamin A storage in a rat model of controlled vitamin A status during aging

It is currently unknown whether the capacity of the liver to esterify and store vitamin A (VA) changes as a function of long-term VA intake or age. The objective of this study was to investigate whether age and/or VA status are factors for the hepatic expression of cellular retinol-binding protein (CRBP), the esterification of retinol by lecithin:retinol acyltransferase (LRAT) and the accumulation of VA and lipids in liver. Two factors, VA intake and age, were studied in a 3x3 design. Diets denoted as VA-marginal, control and supplemented contained 0.35, 4 and 25 mg retinol equivalents/kg diet, respectively; male Lewis rats were fed these diets from weaning until the ages of 2-3 mo (young), 8-10 mo (middle-aged) and 18-20 mo (old) (n = 6/group. Liver CRBP mRNA differed (two-way ANOVA) with dietary VA (P<0.0001) and age (P<0.05). Hepatic LRAT activity increased with dietary VA (P<0.0001). Age was not a factor (P = 0.47) although there was an interaction of age and dietary VA (P<0.0001). Hepatic LRAT activity was correlated (r = 0.633, P<0.0001) with plasma retinol at physiologic concentrations. In VA-supplemented rats of all ages, the plasma molar ratio of total retinol:retinol-binding protein (RBP) exceeded 1, and liver VA and total lipid concentrations were elevated. However, tests of liver function had previously been shown to be within normal values. Thus, the capacity of the liver for retinol esterification by LRAT was not diminished by age or the accumulation of VA and other lipids. We conclude the following: 1) hepatic LRAT activity is regulated across a broad, physiologic range of dietary VA; 2) LRAT activity is regulated throughout life; and 3) the capacity for hepatic VA storage is high throughout life.

Safety of <7500 RE (<25000 IU) vitamin A daily in adults with retinitis pigmentosa

BACKGROUND

Vitamin A supplementation is being used successfully to treat some forms of cancer and the degenerative eye disease retinitis pigmentosa. The daily biological need for vitamin A is estimated to be 800 retinol equivalents (RE)/d (2667 IU/d) for adult women and 1000 RE/d (3300 IU/d) for adult men; doses > or = 7500 RE (> or = 25000 IU)/d are considered potentially toxic over the long term.

OBJECTIVE

We assessed the safety in adults of long-term vitamin A supplementation with doses above the daily biological need but <7500 RE (<25000 IU)/d.

DESIGN

Adults aged 18-54 y with retinitis pigmentosa but in generally good health (n = 146) were supplemented with 4500 RE (15000 IU) vitamin A/d for < or = 12 y (group A) and compared with a similar group (n = 149) that received 23 RE (75 IU)/d (trace group). Mean total consumption of vitamin A in group A was 5583 RE (18609 IU)/d (range: 4911-7296 RE/d, or 16369-24318 IU/d) and that in the trace group was 1053 RE (3511 IU)/d (range: 401-3192 RE/d, or 1338-10638 IU/d).

RESULTS

Patients in group A showed an 8% increase in mean serum retinol concentration at 5 y and an 18% increase at 12 y (P < 0.001); no retinol value exceeded the upper normal limit (3.49 micromol/L, or 100 microg/dL). Mean serum retinyl esters were elevated approximately 1.7-fold at 5 y and remained relatively stable thereafter. No clinical symptoms or signs of liver toxicity attributable to vitamin A excess were detected.

CONCLUSIONS

Prolonged daily consumption of <7500 RE (<25000 IU) vitamin A/d can be considered safe in this age group.

Vitamin A homeostasis and diabetes mellitus

Recent studies have shown that plasma concentrations of vitamin A (retinol) and its carrier proteins, retinol-binding protein (RBP), and transthyretin (TTR), are decreased in human subjects with insulin-dependent (IDDM) but not with noninsulin dependent diabetes mellitus (NIDDM). Rats made diabetic with streptozotocin (STZ) have also been shown to have reduced levels of plasma vitamin A while its hepatic concentrations elevate. The circulatory vitamin A levels remained low while its hepatic concentrations were further elevated following supplementation of the vitamin. The reduced circulatory status of vitamin A in diabetic animals was not caused by its impaired intestinal absorption. Further experimental studies have pointed to the fact that IDDM is associated with a deficiency of vitamin A, which is secondary to an impaired transport mechanism of this vitamin from its hepatic storage to the target site, such as retina of the eyes. The diabetes-associated changes in vitamin A metabolism were reserved to normal by insulin treatment. The underlying cause for decreased metabolic availability in uncontrolled diabetes, is not clearly understood. It appears that the increased hepatic store of vitamin A is attributed to a decreased availability of its carrier proteins. Subnormal vitamin A status in poorly controlled diabetic subjects may not respond to vitamin A supplementation, rather it may increase its load in the liver leading to hepatoxicity. These results clearly suggest that there is need for further research identifying the importance of vitamin A in diabetes mellitus.

Chemoprevention of colorectal tumors: role of lactulose and of other agents

Chemoprevention can be defined as an attempt at cancer control in which the occurrence of the disease is prevented by the administration of one (or more) chemical compounds. Main problems in chemoprevention studies are the choice of a suitable drug, the choice of an appropriate intermediate or definitive end point, and the definition of the population which should be investigated. Main classes of chemopreventive agents include vitamins, non-steroid antinflammatory drugs, minerals such as calcium or selenium, and other antioxidants such as N-acetylcysteine. Chemoprevention is particularly appealing in colorectal cancer, either because these lesions develop through a multistep process, or owing to the concept of "field carcinogenesis'. Between 1985 and 1990 we carried out a controlled study in which antioxidant vitamins or lactulose were used in an attempt to prevent the recurrence of colorectal polyps after their endoscopic removal. Among the 209 patients who could be evaluated, polyps recurred in 5.7% of the individuals who were given vitamins (A, C and E), 14.7% of patients given lactulose and 35.9% of untreated controls (chi 2 = 17.1, P < 0.001). The study suggested that either antioxidant vitamins or lactulose could be effective in reducing the recurrence rate of adenomatous polyps. In a subsequent on-going study, lower doses of the same vitamins were tested versus N-acetylcysteine (600 mg/day) or no treatment. Preliminary results showed a 40% reduction of the recurrence of polyps (versus controls) in individuals given N-acetylcysteine, while the effect of lower doses of vitamins was less appreciable. Definitive results of the study should be available by the end of 1998.

Evaluation of abnormal liver function tests

Although the liver can be affected in a wide range of disorders, the differential diagnosis of abnormal liver function tests can be substantially narrowed by a comprehensive history and physical examination and by the recognition of relatively distinct biochemical patterns of liver injury. Although referral to a specialist may be required for the performance of, for example, percutaneous liver biopsy and long-term management of chronic liver disease, a presumptive diagnosis can usually be made in the vast majority of patients who present to primary care physicians with abnormal liver function tests.

Streptozotocin-induced diabetes in rats is associated with impaired metabolic availability of vitamin A (retinol)

Using streptozotocin-induced diabetic Wistar rats, studies were carried out to examine the metabolic availability of vitamin A in the plasma, liver and the retina of the eye. Control and diabetic rats were fed ad lib. on a semi-purified diet either with or without (basal) vitamin A supplementation, or pair-fed on the basal diet for 4 weeks. Despite the fact that diabetic rats consumed 48% more feed, they had lower plasma concentrations of retinol (P < 0.003). The decrease in plasma retinol concentration was a response to diabetes (or diabetes-induced trauma), since neither pair-feeding (P < 0.01) nor vitamin A supplementation altered this effect (P < 0.05). Furthermore, the hepatic concentrations of the vitamin in these animals remained elevated and this increase was greater in the supplemented diabetic group (P < 0.001). Decreases in 11-cis retinal (a component of rhodopsin) concentrations in the retina were also observed in diabetic animals. The increased hepatic and the decreased plasma and retina vitamin A levels suggest a defect in the transport of the vitamin from the liver.