Professor Bruce Ames, Ph.D., of the University of California, Berkeley is best known as the inventor of the Ames Tests, used worldwide to gauge the carcinogenic potential of natural and synthetic chemicals.
More recently, he's been focused on the role of essential micronutrients –vitamins, minerals, and omega-3 and -6 fatty acids – in aging and disease.
Five years ago, his research led him to propose a new idea – his “triage theory” – that could revolutionize the field (Ames BN 2006).
Nutrient-triage theory of aging
Triage is emergency-care doctors' practice of prioritizing wounded patients for treatment based on the severity of their injuries.
Dr. Ames' triage theory proposes that secondary functions of a micronutrient tend to go unfulfilled when a person's diet doesn't supply more than they need for short-term survival.
high for selenium
All figures are in micrograms (mcg) and come from the USDA or ODS/NIH.
The adult RDA is 55 mcg:
Selenium per 3.5 oz serving
Beef, cooked - 35
Turkey, light meat, roasted - 32
Bread, whole wheat, 1 slice - 10
Albacore Tuna (canned) - 60
Sardines (canned) - 53
Mackerel (canned) - 52
Halibut - 47
Sablefish - 47
Pollock - 47
King Salmon (chinook) - 47
King Crab - 40
Shrimp/Prawns - 40
Silver Salmon (coho) - 38
Sockeye Salmon (red) - 38
Cod - 38
Scallops - 28
Thus, age-related conditions like heart disease, cancer, and dementia could be caused in part as an unintended consequence of otherwise sensible body mechanisms.
It makes sense that when a micronutrient is in short supply, the body would use it only for the nutrient's most essential functions and let others go unperformed.
Dr. Ames believes that if a micronutrient deficiency persists, the body will accumulate gradual, insidious changes that accelerate aging and increase the risk of chronic diseases.
We covered one of Dr. Ames prior studies that support the theory: see “Magnesium Shortage Speeds Aging of America”.
Now, he's turned his attention to selenium, which is an essential component in key immune-system components called selenoproteins … such as selenoprotein P and glutathione peroxidase (GPx).
Selenium study supports unique value of seafood
Selenium seems like a good target for research on the nutrient-triage theory, because of its essentiality to the body's antioxidant network and other anti-cancer mechanisms.
While the evidence linking higher selenium levels to lower cancer risk is mixed (ODS 2011), it is the only mineral that's earned FDA approval to bear a qualified health claim for general cancer prevention.
Drs. McCann and Ames analyzed 25 studies, to examine the activity and blood levels of 12 selenoproteins – five considered essential to short-term survival and seven needed only for long-term health.
They found that the activity and levels of non-essential selenoproteins declined when a person, animal, or microbe was even “modestly” selenium-deficient.
Dr. Ames and McCann noted that the “… same set of age-related diseases and conditions, including cancer, heart disease, and immune dysfunction, are … associated with modest Se [selenium] deficiency …” (McCann JC, Ames BN)
They also pointed out that modest Se deficiency is also associated with genetic malfunctioning of non-essential selenoproteins … which would explain the inconsistent but troubling associations seen between lower selenium intakes and higher risks of cancer, heart disease, or immune disorders.
As the Oakland-based pair concluded, “Modest selenium deficiency is common in many parts of the world; optimal intake could prevent future disease.” (McCann JC, Ames BN 2011)
How much selenium, and from where?
In general, people's selenium levels vary geographically, depending on soil selenium levels, with locally grown produce and grains being the “delivery” vehicles.
As some European countries have switched from generally selenium-rich U.S. grains to generally selenium-poor domestic grains, they've seen their citizens' selenium levels drop.
(The best source of selenium is seafood: see our sidebar, “Seafood scores high for selenium”.)
If we define it as falling short of the adult RDA of 55 micrograms (mcg), outright selenium deficiency is rare in the U.S. and Canada … but quite common in China, which has selenium-poor soils.
However, the results of a recent clinical study suggest that the amount needed to raise body levels of selenoprotein P into the range associated with reduced cancer rates is 105mcg per day (Hurst R et al. 2010).
Participants in that British trial who got 55mcg of selenium daily from a prescribed diet and 50mcg daily from selenium supplements had optimal levels of selenoprotein P, while those who ingested substantially less selenium fell short of that goal.
And the new evidence gleaned through the review by Drs. Ames and McCann supports the Brit's finding from another angle.
The U.S. RDA for selenium is based on the amount needed to maximize blood activities of one form of glutathione peroxidase called GPx3.
But Drs. McCann and Ames found that an essential selenium-dependent protein called Sepp1 was more sensitive to selenium deficiency … which implies a need to raise the RDA:
“The fact that Sepp1 [blood levels are] more sensitive to selenium deficiency than Gpx3 in human plasma [blood] has important implications for estimating the percentage of the population that is modestly selenium deficient … [thus] Sepp1 is expected to be at suboptimal levels, even in some individuals meeting current selenium intake recommendations.”
Accordingly, as the authors noted, “… it recently was suggested that recommended selenium intake levels should be raised from 55 to 75 micrograms per day.”
We second that notion, and would add that, in addition to being a superior source of selenium, seafood is rich in protein, vitamin D, and omega-3s.
Ames BN, Atamna H, Killilea DW. Mineral and vitamin deficiencies can accelerate the mitochondrial decay of aging. Mol Aspects Med. 2005 Aug-Oct;26(4-5):363-78. Review.
Ames BN. Low micronutrient intake may accelerate the degenerative diseases of aging through allocation of scarce micronutrients by triage. Proc Natl Acad Sci U S A. 2006 Nov 21;103(47):17589-94. Epub 2006 Nov 13. Review.
Ames BN. Micronutrients prevent cancer and delay aging. Toxicol Lett. 1998 Dec 28;102-103:5-18. Review.
Ames BN. Optimal micronutrients delay mitochondrial decay and age-associated diseases. Mech Ageing Dev. 2010 Jul-Aug;131(7-8):473-9. Epub 2010 Apr 24. Review.
Fenech M. Micronutrients and genomic stability: a new paradigm for recommended dietary allowances (RDAs). Food Chem Toxicol. 2002 Aug;40(8):1113-7. Review.
McCann JC, Ames BN. Adaptive dysfunction of selenoproteins from the perspective of the triage theory: why modest selenium deficiency may increase risk of diseases of aging. FASEB J. 2011 Mar 14. [Epub ahead of print]
Office of Dietary Supplements (ODS). March 21, 2011. Dietary Supplement Fact Sheet: Selenium. Accessed at http://ods.od.nih.gov/factsheets/selenium
Xun P, Bujnowski D, Liu K, Steve Morris J, Guo Z, He K. Distribution of toenail selenium levels in young adult Caucasians and African Americans in the United States: The CARDIA Trace Element Study. Environ Res. 2011 Feb 10. [Epub ahead of print]