Kim J, et al. Intakes of vitamin A, C, and E, and beta-carotene are associated with risk of cervical cancer: a case-control study in Korea. Nutr Cancer. 2010;62(2):181-9.
This study investigated the influence of antioxidant supplements in 144 cervical cancer patients and 288 age-matched, hospital-based controls. All subjects filled out a questionnaire regarding lifestyle and dietary and supplement intake. Study results indicated that patients with cervical cancer reported a statistically lower mean dietary intake for beta-carotene (p=0.004), vitamin A (p = 0.002), and vitamin C (p<0.001), than control subjects. Total dietary and supplement intake of Vitamin A (p=0.003) and E (p=0.001) were also found to be significantly lower in the cancer patients. Subjects in the highest quartiles were also found to have a statistically significant lower risk for cervical cancer compared to those in the lower quartiles for vitamin A (p<0.001), beta-carotene (p = 0.006), and vitamin C (p=0.001) intake. The authors concluded that total intakes of, vitamins A, C, or E were strongly correlated with a reduced risk for cervical cancer However, they advised that these correlations should be studied in large prospective studies with long- term follow-ups.
Muralikrishnan G, et al. Effects of vitamin C on lipid peroxidation and antioxidant status in tamoxifen-treated breast cancer patients. Chemotherapy. 2010;56(4):298-302.
This study enrolled 60 post-menopausal women with resectable breast cancer to determine the antioxidant effects of Vitamin C. Fifteen normal, healthy women were also enrolled as a control group. The women with breast cancer were divided into 4 groups of 15 who were: not treated with tamoxifen; treated with tamoxifen; treated with vitamin C after 45 days of tamoxifen treatment; or treated with vitamin C after 90 days of tamoxifen treatment. Levels of thiobarbituric acid (TBA) substances (an indicator of lipid peroxidation and oxidative stress) and antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase, and glutathione-S-transferase) were determined in plasma and red blood cell hemolysates. The level of TBA reacting substances was significantly elevated and the levels of antioxidant enzyme were significantly reduced in the untreated and tamoxifen-treated breast cancer patients. However, the authors found that in the groups receiving vitamin C supplementation with tamoxifen, the antioxidant enzyme levels had normalized. The authors concluded that the added antioxidant effect observed with coadministration of Vitamin C may benefit in breast cancer patients receiving tamoxifen treatment.
Sesso, HD, Buring JE, Christen WG, et al. Vitamins E and C in the prevention of cardiovascular disease in men. The Physicians' health study II Randomized Controlled Trial. JAMA. 2008;300(18):2123-2133.
This long-term study sought to evaluate the role of vitamin C or E supplementation in reducing the risk of cardiovascular disease, and involved over 14,000 men aged 50 or older. The participants were randomized to 400 IU of vitamin E every other day or its placebo and 500 mg of vitamin C daily or its placebo. The primary outcome of the study was onset of major cardiovascular events including, nonfatal myocardial infarction, nonfatal stroke, and death from cardiovascular disease.
At the 8-year follow-up, researchers observed the same number of cases in both the vitamin and the placebo groups, with increased risk of hemorrhagic stroke in the vitamin E group. These findings suggest no significant effects of vitamins in lowering the risk of cardiovascular disease as widely believed.
It should be noted that both the vitamins used in the study were synthetic and at much higher levels than those achieved via dietary intake, which may have led to the effects observed. More studies at different doses and involving other populations are warranted to fully assess the role of vitamin supplementation for cardiovascular health.
Slatore CG, Littman AJ, Au DH, et al. Long-term use of supplemental multivitamins, vitamin C, vitamin E, and folate does not reduce the risk of lung cancer. Am J Respir Crit Care Med. 2008;177(5):524-30.
A prospective study of 77,221 men and women (50-76 years) was conducted to determine the association between vitamin use and lung cancer. A total of 521 cases of lung cancer were identified. The findings were based on 10-year average daily use of supplemental multivitamins, vitamin C, vitamin E, and folate. Researchers conclude that vitamin supplementation does not decrease risk of lung cancer. Furthermore, vitamin E use was associated with a slight increase in risk of lung cancer.
Bjelokovic G, Nikolova G, Simonetti RG, et al. Antioxidant supplements for preventing gastrointestinal cancers. Cochrane Database Syst Rev 2004;(4):CD004183.
This is a systematic review of 14 randomized clinical trials. Participants of the studies did not have gastrointestinal diseases but were at high risk of developing gastrointestinal cancer. The outcome measures were incidence of gastrointestinal cancers, overall mortality, and adverse effects. According to the findings of this study, supplementation with beta-carotene, vitamin A, vitamin C, and vitamin E, when taken alone or in combination do not affect incidence of gastrointestinal cancers. Further, they may increase the overall mortality. The effects of Selenium supplementation need confirmation in future randomized trials.
Patients should consult their physicians before initiating vitamin supplementation, especially during and after chemotherapy.
Engelhart MJ, et al. Dietary intake of antioxidants and risk of Alzheimer disease. JAMA 2002;287:3223-9.
A population-based, prospective cohort study evaluating antioxidant intake and risk of developing Alzheimer disease. Subjects (n=5393) were at least 55 years old, free of dementia, noninstitutionalized, and had reliable dietary assessment at baseline. Dietary intake was assessed by self-reported checklist and interview with dietitian using the semiquantitative food-frequency questionnaire (SFFQ). After mean follow-up of 6 years, 146 patients developed Alzheimer disease. After adjustments for age, sex, baseline Mini-Mental State Examination score, alcohol intake, education, smoking habits, pack-years of smoking, body mass index, total energy intake, presence of carotid plaques, and use of supplements, high intake of vitamin C and vitamin E were correlated with lower risk of Alzheimer disease. However, the apparent association may be caused by the influence of a preclinical illness on diet or diet recall/reporting, since the SFFQ itself may indirectly assess cognitive functioning. Furthermore, the multiple comparisons made suggest that some associations may be due to chance and that the critical P value should be set lower than .05.