I have been asked, 'are vitamines helpful for my cancer?', a lot in my clinic. Because vitamin supplements are so popular these days, many people wonder whether vitamin can be helpful against cancer.
Vitamines are essential for our body metabolism. We have to intake them since human body cannot make vitamines by ourselves. Vitamin A is fat-soluble and absorbed by fat globules through the small intestines (see types of vitamines).
There are a lot of data about vitamin A and cancer. I will introduce research data about the relationship between vitamin A supplements and cancer.
Vitamin A contains retinol and carotene, a precursor of retinol. Some carotenoids, most importantly beta-carotene, can be converted to retinol in our body and are sometimes called pro-vitamin A carotenoids. It is found in many vegetables and seeweed. Retinol itself is more absorbable, but mainly exists in animal liver (chikcken liver, pig liver, claw liver, eel liver, etc.).
Vitamin A is important for eye health. It is necessary to generate rhodopsin, the main component of the retina. It also maintains the skin and mucous membrane, preventing infection.
1. Skin cancer, "might be helpful..."
Cancer Epidemiol Biomarkers Prev. 1997 Nov;6(11):949-56.
Effect of retinol in preventing squamous cell skin cancer in moderate-risk subjects: a randomized, double-blind, controlled trial. Southwest Skin Cancer Prevention Study Group.
"Comparing retinol-supplemented subjects with placebo-supplemented subjects showed a hazard ratio for first new SCC of 0.74 (95% confidence interval, 0.56-0.99; P = 0.04). ... Therefore, we concluded that daily supplementation with 25,000 IU of retinol was effective in preventing SCC, although it did not prevent BCC."
In the Retinoid Skin Cancer Prevention Trial (SKICAP) reported two studies about high-risk and intermediate-risk skin cancer, respectively, in 1997. In summary, basal cell carcinoma has no significant correlation with intake of vitamin A, but squamous cell carcinoma has a tendency to decrease when intake vitamin A supplements. It is difficult to conclude because there is not enough evidences, but it might be helpful only to squamous cell carcinoma.
2. Lung cancer, ''It's rather poison to smokers".
Beta-Carotene and Retinol Efficacy Trial (CARET) have conducted clinical trials with retinol, beta-carotene, and placebo for smokers or ex-smokers. The risk of death from lung cancer and incidence of lung cancer was rather increased in the group taking vitamin A over placebo group. In particular, the risk among smokers was a lot higher, leading to early termination of clinical trials.
N Engl J Med. 1996 May 2;334(18):1150-5.
Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease.
"After an average of four years of supplementation, the combination of beta carotene and vitamin A had no benefit and may have had an adverse effect on the incidence of lung cancer and on the risk of death from lung cancer, cardiovascular disease, and any cause in smokers and workers exposed to asbestos."
Other cohort stuides also have similar results. In the study above, smokers, ex-smokers and never-smokers were analyzed separately. The risk of lung cancer was increased with vitamin A supplements in smokers group as in previous CARET stuidy, but the risk was rather decreased with vitamin A in non-smokers group.
In studies using beta-carotene supplementation, these results become more apparent. In a randomized clinical trial with beta-carotene, beta-carotene increased the risk of lung cancer among smokers more significantly than retinol.
Based on these evidences, vitamin A supplement in smokers can increase the risk of lung cancer.
3. Prostate cancer, "can be helpful for someone who lacks vitamin A evidenced by blood test".
Cancer. 1999 Nov 1;86(9):1783-92.
Beta-carotene supplementation for patients with low baseline levels and decreased risks of total and prostate carcinoma.
"These prespecified subgroup analyses appeared to support the idea that beta-carotene supplementation may reduce risk of prostate carcinoma among those with low baseline levels."
There have been studies of prostate cancer with beta-carotene supplements. However, vitamin A has not decreased nor increased the risk of prostate cancer. A study examined beta-carotene serum levels and found that beta-carotene was beneficial among those who had the lowest serum beta-carotene levels.
4. Breast cancer, "significant relationship has not been observed..."
Cancer Causes Control. 2011 Oct;22(10):1383-96. Epub 2011 Jul 15.
Retinol, vitamins A, C, and E and breast cancer risk: a meta-analysis and meta-regression.
"However, associations between other vitamins and breast cancer seem to be limited."
Several studies showed that serum vitamin A levels were low in advanced breast cancer patients. Some researchers performed studies with hypothesis that correction of vitamin A level of breast cancer patients might be helpful against cancer. However, there was no significant correlation between vitamin A intake and breast cancer.
Vitamin A is a fat-soluble vitamin that can be harmful if it taken too much. The recommended daily dose is 5000 IU or 900 μg, and taking more than this dose is not recommended. Cancer patients tend to overdose with vague expectation that they will have anticancer effects due to antioxidant activity. However, the studies above seemed to warn them.
- World Cancer Research Fund & American Institue for Cancer Research. Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective. 2007.
- Moon Te, Levine N, Cartmel B, et al. Effect of retinol in preventing squamous cell skin cancer in moderate-risk subjects: a randomized, double-blind, controlled trial. Southwest Skin Cancer Prevention Study Group. Cancer Epidemiol Biomarkers Prev. 1997 Nov;6(11):949-56.
- Levine N, Moon TE, Cartmel B, et al. Trial of retinol and isotretinoin in skin cancer prevention: a randomised, double-blind, controlled trial. Southwest Skin Cancer Prevention Study Group. Cancer Epidemiol Biomarkers Prev 1997;6:95761.
- 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;334:1150-5
- Paganini-Hill A, Chao A, Ross RK, et al. Vitamin A, beta-carotene, and the risk of cancer: a prospective study. J Natl Cancer Inst 1987;79:443-8.
- Cook NR, Stampfer MJ, Ma J, et al. Betacarotene supplementation for patients with low baseline levels and decreased risks of total and prostate carcinoma.[see comment]. Cancer 1999;86:1783-92.
- Fulan H, Changxing J, Baina WY, et al. Retinol, vitamins A, C, and E and breast cancer risk: a meta-analysis and meta-regression. Cancer Causes Control. 2011;22(10):1383-96.