Briefly, the data from the meta-analysis show that selenium decreases the risk of cancer at the highest daily intake levels of the included studies.
This outcome is consistent with the outcomes of a previous study showing a protective effect of selenium at high doses compared to low doses [Cai 2016]. A 2018 meta-analysis used different methods to assess selenium exposure and showed a null association between selenium at high doses compared to low doses [Vinceti 2018].
Selenium Protection Against Cancer May Vary with the Form of the Cancer
The data from the 37 observational and intervention studies included in the 2020 meta-analysis showed the following associations [Kuria 2020].
Selenium intakes at doses above 55 micrograms per day were associated with a decreased risk of all cancers
The protective effects of the selenium on specific cancers varied.
Some cancers showed a significantly decreased risk:
- Esophagus
- Liver
- Pancreas
- Stomach
Some cancers showed a statistically non-significant increased risk:
- Bladder
- Breast
Skin cancer showed increased risk initially, but that association disappeared after researchers controlled for such confounding variables as age, BMI and smoking.
Selenium and Prostate Cancer: 2018 Meta-Analysis
The authors of a 2018 meta-analysis of 38 studies of the association between selenium intakes and the risk of prostate cancer concluded that selenium most probably has a protective role against development of prostate cancer and its progression to advanced stages. They agreed that selenium supplementation can be proposed for prevention of prostate cancer [Sayehmiri 2018].
The 2018 meta-analysis included data from 36,419 cases and 105,293 controls. The pooled relative risk of the relationship between selenium and prostate cancer was 0.86. Relative risks based on serum, plasma, and nail samples of selenium status were 0.69, 0.85, and 0.66, respectively.
According to the data from 10 studies, the association between selenium intake/status and the incidence of advanced prostate cancer 0.67.
Note: A relative risk of 1.00 would have meant that the risk of getting prostate cancer was equal in the higher selenium intake/status groups and the lower selenium intakes/status groups. That the relative risks were statistically significantly under 1.00 indicates a reduced risk of prostate cancer is associated with higher selenium intake/status.
Selenium Intakes/Status and Lung Cancer: Cochrane Review
The authors of a 2020 Cochrane Database review concluded that selenium in men results in little to no difference in lung cancer incidence and lung cancer mortality [Cortés-Jofré 2020]. However, their conclusion is based on an analysis of data from a single randomized controlled trial, the SELECT trial, in which a synthetic selenomethionine supplement was used instead of a natural selenium-enriched yeast supplement and in which the study participants had high baseline selenium status (mean: 135 mcg/L) [Lippman 2009].
There is good reason to think that the selenium-enriched yeast supplement is the preferred supplement form [Richie 2014]. The high-selenium yeast supplements contain multiple species of selenium in addition to selenomethionine; selenium species other than selenomethionine may result in decreases in oxidative stress and in reductions in cancer incidence. One or more of these other species of selenium may have cancer protective effects.
Take Home Message: Selenium Intakes and Cancer
The authors of the selenium intakes and cancer risk meta-analysis wrote:
“The results from our meta-analysis suggest that at the highest daily intake levels of the included studies, selenium decreases the risk of cancer” [Kuria 2020, p. 689].
“Additional selenium from supplements showed a significant protective effect unlike selenium from food only. This indicates that extra intake of selenium other than food might be essential for cancer prevention” [Kuria 2020, p. 692].
Sources
Cai X, Wang C, Yu W, et al. Selenium Exposure and Cancer Risk: An Updated Meta-analysis and Meta-regression. Sci Rep. 2016;6:19213.
Cortés-Jofré M, Rueda JR, Asenjo-Lobos C, Madrid E, Bonfill Cosp X. Drugs for preventing lung cancer in healthy people. Cochrane Database Syst Rev. 2020;3(3):CD002141.
Kuria A, Fang X, Li M, et al. Does dietary intake of selenium protect against cancer? A systematic review and meta-analysis of population-based prospective studies. Crit Rev Food Sci Nutr. 2020;60(4):684-694.
Lippman SM, Klein EA, Goodman PJ, et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2009;301(1):39-51.
Richie JP Jr, Das A, Calcagnotto AM, et al. Comparative effects of two different forms of selenium on oxidative stress biomarkers in healthy men: a randomized clinical trial. Cancer Prev Res (Phila). 2014;7(8):796-804.
Sayehmiri K, Azami M, Mohammadi Y, Soleymani A, Tardeh Z. The association between Selenium and Prostate Cancer: a Systematic Review and Meta-Analysis. Asian Pac J Cancer Prev. 2018;19(6):1431-1437.
Vinceti M, Filippini T, Del Giovane C, et al. Selenium for preventing cancer. Cochrane Database Syst Rev. 2018;1(1):CD005195.
The information presented in this review article is not intended as medical advice and should not be construed as such.
31 August 2020