China study affirms the strong anti-senility potential of selenium from seafood and other sources
by Craig Weatherby
Alzheimer's disease is the most common form of dementia, affecting more than 4.5 million Americans: a number that could reach 16 million by 2050.
The cost of caring for Alzheimer patients in the US now exceeds $100 billion, and the combined Medicare and Medicaid costs for beneficiaries with Alzheimer’s may increase to $184 billion by 2010.
As a consequence, any dietary intervention that could reduce the risk of Alzheimer’s and other forms of senile dementia should be brought to people’s attention.
Selenium is an essential component of some of the body’s key antioxidant enzymes, which are believed to help reduce formation of the brain plaques that characterize Alzheimer’s disease and destroy brain cells.
High selenium intake is also associated with lower risk of arteriosclerosis, and may reduce the risk of cancer.
The richest food sources of selenium are seafood (See “Selenium and seafood”, below; only Brazil nuts contain more selenium per ounce).
Earlier this year we summarized the findings of a nine-year study from France, in which higher blood selenium levels were associated with a substantially reduced risk of developing signs of Alzheimer’s or other forms of dementia (See “‘Seafood Mineral’ Selenium May Reduce Risk of Senility”).
And the recently published results of a study from China seem to support the value of selenium in preventing senility.
Selenium gets more support as anti-Alzheimer’s agent
Researchers from the Indiana University School of Medicine examined 2,000 elderly Chinese people—average age 72, and 54 percent women—most of who had lived in the same village all their lives (Gao S et al 2007).
The Indiana University team, led by Dr. Sujuan Gao, analyzed the selenium levels of nail samples collected from the villagers, and divided them into five groups, according to selenium content.
They then subjected the participants to a battery of cognitive function tests.
The results showed that the villagers with the highest selenium levels enjoyed the lowest rates of dementia.
The researchers also found that rates of dementia corresponded closely to selenium levels, in a “dose-dependent” manner: a correlation that supports the hypothesis that higher selenium intake yields a reduced risk of dementia, and that low selenium intake raises the risk.
As Dr. Gao’s team wrote, “Lower selenium levels measured in nail samples were significantly associated with lower cognitive scores… Results in this geographically stable cohort support the hypothesis that a lifelong low selenium level is associated with lower cognitive function” (Gao S et al 2007).
Sustained intake seen as essential
While the new findings are encouraging, the Indiana researchers noted that the brain metabolizes selenium slowly, so one would need to sustain an increase in one’s selenium intake for several years in order to exert a substantial senility-prevention impact.
In addition, the areas of the brain that take the longest to mature are the ones that show early signs of Alzheimer's, which suggests that people need to maintain ample selenium intake throughout their lives.
Selenium and seafood
People get most of their dietary selenium from grains grown in selenium-rich soils. While soils in the upper Midwest, Northeast, Florida, and Northwest are selenium-poor, soils throughout most of the US grain belt—the states between the Mississippi and the Rockies—are high in selenium.
But the best common dietary sources of selenium, by far, are ocean fish. The US recommended daily allowance (RDA) for selenium is 55 micrograms (mcg), for men and women aged 19 or older.
As shown in the table below, the seafood species we offer are high in selenium, with a 3.5 ounce serving of each providing from 95 percent (sardines) to 50 percent (scallops) of an adult’s daily needs.
Sardines King Salmon Halibut Tuna** Sablefish King Crab Silver Salmon Sockeye Salmon Sockeye, canned Scallops 52.7 46.8 46.8 46.8 46.8 40.0 38.0 37.8 34.3 27.9
*micrograms (mcg) of selenium. US RDA = 55 mcg. Source: USDA nutrient database at http://www.ars.usda.gov/main/site_main.htm?modecode=12354500
**This is the selenium content for Yellow fin, Skipjack and Blue fin tuna in the USDA database, which provides no nutrient data for Albacore tuna. Since its diet is similar to that of other tuna, it probably contains comparable amounts of selenium.
Selenium: seafood’s built-in anti-mercury safeguard
Selenium binds to the methylmercury in seafood and renders it harmless: a fact that may explain why a large study in the Seychelles Islands, where children eat 12 times more fish than their American counterparts, found no developmental deficits associated with mercury intake (See “Mercury-Fighting Mineral in Fish Overlooked”).
Dr. Nicholas Ralston of the University of North Dakota tested various fish and found that the species most commonly consumed by Americans—including grouper, pollock, tuna, salmon, and flounder—all had much more selenium than mercury. For example, albacore tuna has 15 times more selenium than mercury.
This is not to say that the issue is entirely settled, or that pregnant and nursing mother and young children should eat high-mercury species. But it does appear that selenium is a major, overlooked factor in the ongoing debate over mercury and fish, in which more heat than light has been shed.
- Akbaraly NT, Hininger-Favier I, Carriere I, Arnaud J, Gourlet V, Roussel AM, Berr C. Plasma selenium over time and cognitive decline in the elderly. Epidemiology. 2007 Jan;18(1):52-8.
- Berr C, Balansard B, Arnaud J, Roussel AM, Alperovitch A. Cognitive decline is associated with systemic oxidative stress: the EVA study. Etude du Vieillissement Arteriel. J Am Geriatr Soc. 2000 Oct;48(10):1285-91.
- Berr C, Richard MJ, Roussel AM, Bonithon-Kopp C. Systemic oxidative stress and cognitive performance in the population-based EVA study. Etude du Vieillissement Arteriel. Free Radic Biol Med. 1998 May;24(7-8):1202-8.
- Burguera JL, Burguera M, Gallignani M, Alarcon OM, Burgueera JA. Blood serum selenium in the province of Merida, Venezuela, related to sex, cancer incidence and soil selenium content. J Trace Elem Electrolytes Health Dis 1990;4:73-7.
- Fleet JC. Dietary selenium repletion may reduce cancer incidence in people at high risk who live in areas with low soil selenium. Nutr Rev 1997;55:277-9.
- Gao S, Jin Y, Hall KS, Liang C, Unverzagt FW, Ji R, Murrell JR, Cao J, Shen J, Ma F, Matesan J, Ying B, Cheng Y, Bian J, Li P, Hendrie HC. Selenium Level and Cognitive Function in Rural Elderly Chinese. Am J Epidemiol. 2007 Jan 31; [Epub ahead of print]
- Hebert LE, Scherr PA, Bienias JL, Bennett DA, Evans DA. Alzheimer disease in the US population: prevalence estimates using the 2000 census. Arch Neurol. 2003 Aug;60(8):1119-22.
- Knekt P, Marniemi J, Teppo L, Heliovaara M, Aromaa A. Is low selenium status a risk factor for lung cancer? Am J Epidemiol 1998;148:975-82.
- Lapenna D, de Gioia S, Ciofani G, Mezzetti A, Ucchino S, Calafiore AM, Napolitano AM, Di Ilio C, Cuccurulo F. Glutathione-related antioxidant defenses in human atherosclerotic plaques. Circulation 1998;97:1930-4.
- Mendelsohn AB, Belle SH, Stoehr GP, Ganguli M. Use of antioxidant supplements and its association with cognitive function in a rural elderly cohort: the MoVIES Project. Monongahela Valley Independent Elders Survey. Am J Epidemiol. 1998 Jul 1;148(1):38-44.
- Neve J. Selenium as a risk factor for cardiovascular diseases. J Cardiovasc Risk 1996;3:42-7.
- Ozer NK, Boscoboinik D, Azzi A. New roles of low density lipoproteins and vitamin E in the pathogenesis of atherosclerosis. Biochem Mol Biol Int 1995;35:117-24.
- Patterson BH and Levander OA. Naturally occurring selenium compounds in cancer chemoprevention trials: A workshop summary. Cancer Epidemiol Biomarkers Prev 1997;6:63-9.
- Russo MW, Murray SC, Wurzelmann JI, Woosley JT, Sandler RS. Plasma selenium levels and the risk of colorectal adenomas. Nutr Cancer 1997;28:125-9.
- Shamberger RJ. The genotoxicity of selenium. Mutat Res 1985;154:29-48.
- WHO (World Health Organization). Neurological disorders affect millions globally: WHO report. Accessed online March 2, 2007 at http://www.who.int/mediacentre/news/releases/2007/pr04/en/index.html.
- Young KL and Lee PN. Intervention studies on cancer. Eur J Cancer Prev 1999;8:91-103.