Saturday, January 03, 2009

Beta-carotene risks over-stated

Beta-carotene risks over-stated By Neil E. Levin, CCN, DANLA A recent journal article pointed out the widely-reported danger of smokers using beta-carotene, a natural source (provitamin) of vitamin A, as part of their multivitamins. 1 In this meta-analysis the researchers have neglected to consider pre-existing dietary and serum levels of this nutrient, making their claim to control by placebo inadequate to properly isolate this variable. In fact, this failure to determine the effects of beta-carotene at a dose-dependent plasma level – and by neglecting to measure total beta-carotene intake along with the relevant synergistic antioxidants associated with it, as opposed to simply measuring supplemental intake - raises serious questions about the validity of these results. 2 There is also legitimate scientific debate over the use of trans versus cis forms of this provitamin that may affect the way it is used in vivo that dispute whether all forms are equal, which most studies simply do not address (including this meta-analysis). 3 Regarding beta-carotene safety little has been satisfactorily resolved, and the negative studies have been vigorously disputed for these and other reasons. For example, researchers have previously noted in the Journal of the National Cancer Institute that beta-carotene has been shown to not affect the risk of oxidative DNA damage in male smokers, despite its reputation as an antioxidant. But neither did the provitamin A prove to cause oxidative DNA damage. 4 It has become apparent to numerous observers that simply measuring supplementation of beta-carotene is not a good predictor of serum levels or of risk, and that a low level of total antioxidant intake may be a more valid marker in this regard. In fact, the dietary level of several antioxidants has been shown to be an independent predictor of plasma beta-carotene, especially in moderate alcohol drinkers. A recent study reports, “This may explain, at least in part, the inverse relationship observed between plasma beta-carotene and risk of chronic diseases associated to high levels of oxidative stress (i.e., diabetes and CVD), as well as the failure of beta-carotene supplements alone in reducing such risk.” 2 As the authors (Tanvetyanon, et al) of this current analysis have themselves noted, the Physicians Health Study compared the effects of taking 50 mg of supplemental beta-carotene (over 83,000 IU) every other day to a placebo in 22,071 US male physicians aged 40-84 and found no adverse health effects over a 12-year study period. 5 Likewise, the Women’s Health Study of 39,876 health professionals found no significant difference on lung cancer rates when looking at the effects of 50 mg of beta-carotene administered on alternate days over 2+ years plus a 4 year follow up period, using forms and dosing similar to the Physician’s Health Study to achieve very high serum levels of beta-carotene. 6 In a third study used in the current meta-analysis, The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group (ATBC), an antioxidant study in Finland was halted early because of a widely reported small increase in cancer rates among male smokers taking beta-carotene that were only possibly linked to that nutrient. 7 Headlines associated this supplement with cancer risk. Despite objections that the study was flawed, beta-carotene use dropped. This study continues to be widely cited and believed, despite the researchers’ own statements that the results were most likely due to chance. A later analysis published in July 2004 took another look at that same Finnish smokers study’s data, but now taking into account total antioxidant intake, which should have cleared away some of the scientific controversy over beta-carotene. The smokers’ risk of getting lung cancer was inversely associated with total antioxidants in the diet, with more total antioxidants resulting in fewer cancers. 8 In this study a composite antioxidant index was generated for each of the 27,000 men over 14 years. The calculated amounts of carotenoids, flavonoids, vitamin E, selenium and Vitamin C were compared to actual lung cancer rates, with a clear result: a combination of antioxidants lowered lung cancer risk in male smokers. Properly reviewed, beta-carotene was not the culprit; low antioxidant status was the more relevant factor affecting cancer rates, and supplementation with a single antioxidant supplement simply failed to create enough improvement to avert deaths related to oxidative factors. Perhaps the supplementation with beta-carotene was simply a case of “too little, too late”, rather than a root cause of a slightly higher lung cancer rate in those smokers. It is notable that Tanvetyanon et al included the ATBC study but failed to even reference the later Wright et al study that largely refuted the alleged harms of beta-carotene shown in ATBC, which were shown to be more likely due to low levels of total antioxidant intake than to excessive beta-carotene intake. This later review of ATBC should be a cautionary tale concerning the lack of proper controls in nutrient studies, especially as compounded by the use of meta-analysis, and should have alerted the current authors to that all-too-common mistake in nutrient study design. Indeed, another large study has noted that high carotenoid intake, confirmed by measures of plasma, was associated with lower mortality rates among the elderly over a ten year period. 9 This model measured results of consuming both supplements and foods, not solely supplement input, and when combined with plasma levels should therefore be regarded as a far more robust type of science for measuring vitamin effects than a meta-analysis of simply supplementation. As in the long-term Physicians Health Study, there was no observable risk of lung cancer noted in this report. The fourth study used in the current meta-analysis used very high doses of both beta-carotene (30 mg, equal to 50,000 IU) plus 25,000 IU of pre-formed vitamin A. 10 These amounts are extremely high; the Upper Limit for vitamin A is 10,000 IU, though there is none for beta-carotene because of its historic safety record. The amount of beta-carotene used in the eye vitamins were high only because the authors selected solely formulas designed for eye health that typically provide more beta-carotene than ordinary multivitamins. This distinction is not clear in their calling such formulas “multivitamins”, because that name is typically given to full-spectrum formulas containing a full range of the essential vitamins with minerals, not system-specific formulas like those sold for eye health. Such formulas have proved to be beneficial in maintaining eye health and the combination of antioxidants have been stronger antioxidants than beta-carotene, which is potentially a pro-oxidant at times and could thus be used more safely – and effectively - in combination with other antioxidants. 11 Most importantly, the authors have not shown why they assume that “multivitamin” use would be associated with the supposed risks of beta-carotene used singly, even if those risks for the solo provitamin are assumed to be true. Nor have they adequately demonstrated the alleged dangers of taking eye formula supplements, or even the danger of lung cancer rates increasing in those taking mixtures of beta-carotene combined with other antioxidant nutrients. In the case of multivitamins most studies have shown overwhelmingly positive effects, such as one report evidencing reduced infections in nursing homes with vitamins over placebo (73% vs. 43%; P < 0.001). Intervention was with a multivitamin containing beta-carotene. Infection-related absenteeism was higher in the placebo group than in the treatment group (57% vs. 21%; P < 0.001). Perhaps most importantly, 93% of participants with diabetes mellitus reported an infection versus only 17% of those receiving supplements (P < 0.001). 12 These huge reductions in potentially serious infections among our elderly citizens should be measured against the relatively slight and mostly theoretical risk of increased lung cancer rates associated with beta-carotene supplementation. A study reported in the Journal of the National Cancer Institute looked at death rates in a population given multivitamins or other nutrients. 13 After supplements were given for 5.25 years in the general population trial of 30,000 people, significant reductions in total [relative risk (RR) = 0.91] and cancer (RR = 0.87) mortality were observed in subjects receiving beta-carotene, alpha-tocopherol, and selenium combined. The same researchers reported on a subgroup of 3,318 persons with esophageal Dysplasia (a precursor to esophageal cancer) that was given either a multiple vitamin-and-mineral supplement or a placebo for 6 years. In this portion of the trial, small reductions in total (RR 0.93) and cancer (RR = 0.96) mortality were observed but were not significant. In any case, no increase in cancer rates was noted in the group taking multivitamins; there was actually a possible small benefit in terms of reducing this risk. The participants getting the multivitamin took a daily beta-carotene capsule along with two multivitamin tablets. This was a group of subjects at high risk of getting throat cancer. 14-15 It is a leap of faith to assume that a single nutrient would have identical effects to a combination of nutrients without substantial supporting evidence, which is still lacking; confounded by conflicting evidence and multiplying variables in meta-analyses. Since nutrients are both synergistic and present in the diet, it is important to factor those known variables into a proper study design. All too often, researchers do not consider this fundamental difference between drug and nutrient research and unwittingly introduce extra variables that undermine their conclusions. 16 This current meta-analysis of 4 studies - only one of which unquestionably shows a slight increase in lung cancer risk but does not actually measure isolated beta-carotene risk; two others are well-designed and robust studies looking at serum levels of those taking a high dose of beta-carotene but show no increased risk in lung cancer rates, and the fourth has been largely shown to be moot by a later and more complete re-analysis of the data - does not support the hypothesis that beta-carotene increases rates of lung cancer and that multivitamins are therefore dangerous. Thus, there is no sound basis in the current review for suggesting that warning labels may be needed for multivitamins or eye health supplements containing beta-carotene along with other nutrients that have been shown in well-designed studies to help protect the eyesight – and independence - of our aging population. REFERENCES: Tanvetyanon T, Bepler G. Beta-carotene in multivitamins and the possible risk of lung cancer among smokers versus former smokers: a meta-analysis and evaluation of national brands. Cancer. 2008 Jul 1;113(1):150-7. PMID: 18429004 Valtueña S, et al. The total antioxidant capacity of the diet is an independent predictor of plasma beta-carotene. Eur J Clin Nutr. 2007 Jan;61(1):69-76. Epub 2006 Jul 12. PMID: 16835597 [Supported by the European Community IST-2001–33204 'Healthy Market', the Italian Ministry of University and Research COFIN 2001 and the National Research Council CU01.00923.CT26 research projects.] Andreas Schieber, Reinhold Carle. Occurrence of carotenoid cis-isomers in food: Technological, analytical, and nutritional implications. Trends in Food Science & Technology, Volume 16, Issue 9, September 2005, Pages 416-422 van Poppel G, Poulsen H, Loft S, Verhagen H. No influence of beta carotene on oxidative DNA damage in male smokers. J Natl Cancer Inst. 1995 Feb 15;87(4):310-1. PMID: 7707423 Hennekens CH, Buring JE, Manson JE, et al. Lack of effect of long-term supplementation with beta carotene on the incidence of malignant neoplasms and cardiovascular disease. N Engl J Med. 1996 May 2;334(18):1145-9. PMID: 8602179 Lee IM, Cook NR, Manson JE, Buring JE, Hennekens CH. Beta-carotene supplementation and incidence of cancer and cardiovascular disease: the Women's Health Study. J Natl Cancer Inst. 1999 Dec 15;91(24):2102-6. PMID: 10601381 The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. N Engl J Med. 1994 Apr 14;330(15):1029-35. PMID: 8127329 Wright ME, et al. Development of a comprehensive dietary antioxidant index and application to lung cancer risk in a cohort of male smokers. Am J Epidemiol. 2004 Jul 1;160(1):68-76. PMID: 15229119 Buijsse B, et al. Plasma carotene and alpha-tocopherol in relation to 10-y all-cause and cause-specific mortality in European elderly: the Survey in Europe on Nutrition and the Elderly, a Concerted Action (SENECA). Am J Clin Nutr. 2005 Oct;82(4):879-86. PMID: 16210720 Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med. 1996;334:1150–1155. Bartlett H, Eperjesi F. Age-related macular degeneration and nutritional supplementation: a review of randomised controlled trials. Ophthalmic Physiol Opt. 2003 Sep;23(5):383-99. Review. PMID: 12950886 Liu BA, et al. Effect of multivitamin and mineral supplementation on episodes of infection in nursing home residents: a randomized, placebo-controlled study. J Am Geriatr Soc. 2007 Jan;55(1):35-42. Erratum in: J Am Geriatr Soc. 2007 Mar;55(3):478. PMID: 17233683 Blot WI, Li IY, Taylor PR, et al. Nutrition intervention trials in Linxian, China: supplementation with specific vitamin/mineral combinations, cancer incidence, and disease-specific mortality in the general population. J Natl Cancer Inst 1993:8ı:1483-92 Li JY, Taylor PR, et al. Nutrition intervention trials in Linxian, China: multiple vitamin/mineral supplementation, cancer incidence, and disease-specific mortality among adults with esophageal dysplasia. J Natl Cancer Inst. 1993 Sep 15;85(18):1492-8. PMID: 8360932 Blot WI, et al. The Linxian trials: mortality rates by vitamin-mineral intervention group. Am J Clin Nutr. 1995 Dec;62(6 Suppl):1424S-1426S. PMID: 7495242

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