Selenium is linked (again) with lower risk of cancer; seafood is richest source of a mineral that can make an FDA-approved cancer health claim
by Craig Weatherby
Why are we running a photo of CNN's Anderson Cooper?
During last year's Presidential race, he had a spot of skin cancer removed from under his eye.
The high public profile of skin-cancer patients like Cooper and Senator John McCain amplify the real but overblown threat of skin cancer from sun exposure.
In fact, that threat appears to be far outweighed by the overall anti-cancer benefits of vitamin D, which is generated when UV sunrays strike the skin.
For more on that topic see our 2007 article, “Cancer Society’s Anti-Sun Ads Decried as Deceptive.”
Now, adding another kind of cancer to the mineral's previously documented preventive potential (see the links at the end of this article), the findings of a new study suggest that selenium-rich diets may bolster protection from skin tumors.
Selenium and cancer
Selenium is developing a reputation as an anti-cancer nutrient, based on evidence from epidemiological and clinical studies.
Those findings could be explained by the mineral’s role in the structure and function of key immune system enzymes, though selenium's anti-cancer mechanisms remain unclear.
Selenium is integral to dozens of “seleno-proteins” in the body, including antioxidant enzymes critical to relevant immune functions.
Two clinical trials and several large epidemiological studies have linked selenium with lower cancer rates, which is why selenium supplements can bear this FDA-approved statement:
“Selenium may reduce the risk of certain cancers. Some scientific evidence suggests that consumption of selenium may reduce the risk of certain forms of cancer. However, FDA has determined that this evidence is limited and not conclusive.”
(Calcium and antioxidant vitamins are the only other nutrients permitted to make a similar “qualified health claim” related to cancer.)
|Seafood is rich in selenium|
Algae, seaweed, and aquatic plants absorb selenium and pass it up the ocean food chain to fish and shellfish.
In fact, ocean fish are the best food sources of selenium by far, exceeded only by Brazil nuts.
All figures below are in micrograms (mcg) and come from USDA data tables for cooked seafood, or canned where noted.
The US RDA is 55 mcg, and few other food sources even come close to these levels per serving:
- Selenium per 3.5 oz
- Albacore Tuna (canned) 60
- Sardines (canned) 52.7
- Mackerel (canned) 51.6
- Halibut 46.8
- Sablefish 46.8
- Pollock 46.8
- King Salmon (chinook) 46.8
- King Crab 40
- Shrimp/Prawns 39.6
- Silver Salmon (coho) 38
- Sockeye Salmon (red) 37.8
- Cod 37.6
- Scallops 27.9
However, a large clinical trial published this year found no drop in cancer rates among men who took selenium supplements (Lippman SM et al. 2009).
This finding contradicts those of many epidemiological studies that link higher selenium intake via foods to lower rates of common cancers.
The more positive findings from epidemiological studies could reflect the added, synergistic benefits of other anti-cancer nutrients present in selenium-rich foods.
In fact, it seems unsurprising that selenium obtained naturally from whole foods appears more protective in studies than does the same amount of selenium obtained from supplements.
For example, in addition to selenium, fatty ocean fish are high in vitamin D and omega-3s… a demonstrably immune-supportive duo.
(Omega-3s may blunt the burning effects of UV sunrays: see “Dietary Fish Oil Found to Deflect Sun Damage.”)
Selenium is again making headlines with regard to the mineral’s protective potential, which we reviewed last year (see “Can Selenium Curb Cancer?”).
This time, the results of a new study suggest that selenium may help reduce the incidence of skin cancer.
New study affirms selenium’s anti-cancer potential
More than 1.5 million Americans receive a skin cancer diagnosis every year.
And according to a new epidemiological study from Dutch and Australian researchers, higher blood levels of selenium may reduce the incidence of skin cancer by about 60 percent.
The bi-national team reported that higher blood levels of selenium were associated with reduced risks of the two dominant forms of skin cancer: basal cell carcinoma (BCC) and squamous cell carcinoma (SCC).
In contrast, blood levels of carotenoids (e.g., beta-carotene) and alpha-tocopherol (part of the vitamin E complex) had no apparent influence on skin cancer risks.
The Dutch-Australian group examined 485 adults randomly chosen from an Australian community, who gave blood samples in 1996 and had their health status examined and recorded in 2004.
The researchers found significant associations betweenhigher selenium levels and a lower risk of having developed skin cancer over that eight-year period.
The highest average selenium levels were associated with a 57 percent reduction in the incidence of BCC, and a 64 percent reduction in the incidence of SCC, compared to the lowest average selenium levels.
The higher, seemingly protective levels were between 1.3 and 2.8 micromoles per liter, and the lower, riskier levels ranged between 0.4 and 1.0 micromoles per liter.
Frankly, we do not know exactly how much dietary selenium it takes to reach the seemingly beneficial blood level range.
The adult RDA is 55mcg, but it makes sense to more than that minimum, up to the safe intake limit of 400mcg per day for adults (For full intake guidance, see the selenium entry in the NIH supplement database).
To be clear, epidemiological studies like the one we report today cannot establish a cause-effect relationship between selenium and reduced cancer rates.
That said, these findings fit with prior studies, and with what we know about the role of free radicals in skin cancer and selenium’s essential role in forming many key immune-system enzymes.
Eat ocean fish!
- van der Pols JC, Heinen MM, Hughes MC, Ibiebele TI, Marks GC, Green AC. Serum antioxidants and skin cancer risk: an 8-year community-based follow-up study. Cancer Epidemiol Biomarkers Prev. 2009 Apr;18(4):1167-73. Epub 2009 Mar 31.
- Heinen MM, Hughes MC, Ibiebele TI, Marks GC, Green AC, van der Pols JC. Intake of antioxidant nutrients and the risk of skin cancer.Eur J Cancer. 2007 Dec;43(18):2707-16. Epub 2007 Nov 7.
- Lippman SM, 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 Jan 7;301(1):39-51. Epub 2008 Dec 9.