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Biomedical Bulletin
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Scottish IQ Study Confirms
Cognitive Value of Fish Oil

mportant new research from Scotland clearly confirms that when people consume optimal amounts of omega-3 fatty acids, their cognitive function – especially their memory – improves significantly.1 In other words, when your grandmother told you that fish was “brain food,” she was right.

Since the typical Scottish diet includes lots of oily fish, Scotland is an ideal laboratory for evaluating the effects of dietary fish oils, especially omega-3 polyunsaturated fatty acids (PUFAs), on health, cognition, and longevity. The roots of this study go back over a half-century, when a group of prescient educators decided to measure the IQ of every 11-year-old child living in Scotland in 1947. More than 50 years later, in 2000-2001, the Aberdeen and Edinburgh researchers were able to pull together the IQ scores of about 350 of these children, track down many of them – now in their mid-60s – and test their cognitive and mental functions all over again. At the same time, they evaluated their diets and measured the omega-3 content of their red blood cells, providing an objective – though indirect – estimate of PUFA content in their diet.

The availability of childhood IQ data from a large homogenous elderly population afforded a unique opportunity to examine just what the years can do to a person’s ability to think and remember. What effect, if any has their diet – particularly their intake of fish oil and vitamins – had on their cognitive or mental abilities?

11-Point Fish-Oil IQ Advantage

The results of the study were striking. Although both fish-oil users and non-users started out at age 11 with the same IQ (~100), by age 64, those who regularly consumed fish oil (and possibly other nutrient supplements) enjoyed an 11-point cognitive advantage over a group of matched controls who had not regularly included significant amounts in their diet. By age 64, fish-oil users had gained nearly 6 IQ points over their childhood scores, while non-users had actually lost 5 points (see figure).

Importantly, fish-oil users did significantly better (P <0.05) on two important subtests: digit symbol and block design. These measures are particularly sensitive to cognitive aging and early signs of Alzheimer’s disease. They can pick up even mild cognitive impairment, and when combined, can help predict the likely progress of dementia with a reasonable degree of precision. These results are just the latest in a long line of research studies demonstrating significant advantages of omega-3 fatty acid consumption for optimal mental and cognitive function, not to mention for maintaining cardiovascular health and possibly preventing certain cancers. For example, consuming omega-3s has been shown to reduce the risks associated with heart attacks, cardiac arrhythmias, angina pectoris, stroke, and death.2,3

The two most important omega-3 fatty acids for cardiovascular and mental health are DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid). DHA is considered particularly beneficial, because it is a primary component of the phospholipids that constitute neuronal cell membranes. A deficiency in brain DHA can compromise the integrity of these membranes, whereas increasing DHA consumption restores phospholipid levels to normal.4,5

Omega-3s Reduce Alzheimer’s Risk

One recent study found that the omega-3 fatty acid levels in the plasma phospholipids of people with Alzheimer’s disease were 30% to 40% lower than those in healthy, age-matched controls.6 Two prospective studies indicated that diets high in saturated fats and cholesterol (eg, rich in meat and dairy products) increase the risk of dementia, whereas fish-rich diets may decrease this risk.7,8

In another study of 815 randomly selected people, aged 65 to 94 years, the risk of developing Alzheimer’s disease was inversely proportional to the dietary intake of fish. When the data were corrected for the influence of age, sex, race, educational level, and certain genetic and other factors, it turned out that those who ate fish as little as one to three times per month had a 40% lower relative risk of Alzheimer’s disease than those who never ate fish, and those who ate fish once per week had a 60% lower risk.9

Let Them Eat Fish?

These findings might well entice you to rush out to the nearest fish market. And you probably should, because fish is a terrific food in many ways. Bear in mind, though, that today’s fish can have their downside, and eating too much of certain kinds may not be such a good idea. Although fish are generally an excellent source of high-quality protein and healthful fats, many popular fish also contain high levels of environmental toxins, notably polychlorinated biphenyls (PCBs), which are carcinogenic; and organic mercury compounds, which can cause serious neurologic damage, in addition to promoting atherosclerosis and heart disease.

The National Academy of Sciences now recommends that pregnant women and women who may become pregnant completely avoid eating fish with the highest levels of methylmercury, such as king mackerel, tilefish, shark, and swordfish. Other fish, including tuna, salmon, haddock, cod, pollack, and sole, may also contain mercury, but at lower levels. Local contamination of rivers and lakes may also be problematic, and even farm-raised fish may be exposed to pollution and contaminated feed. Thus, the substantial cardiovascular and neurologic benefits we used to take for granted from eating fish may be at least partially negated by environmental contamination.10,11

Even in the face of essential fatty acid deficiencies and the many other deleterious effects of living, such as poor diet, impaired circulation, chronic inflammation, free radical exposure, drug side effects, and reduced neuronal functioning, there is much we can do to provide the brain with the nutrients it needs to continue working optimally. For example, foods and supplements containing optimal ratios of omega-3 PUFAs are readily available and provide an excellent, reliable source of high-quality EPA and DHA.

References

  1. Whalley LJ, Fox HC, Wahle KW, Starr JM, Deary IJ. Cognitive aging, childhood intelligence, and the use of food supplements: possible involvement of n-3 fatty acids. Am J Clin Nutr. 2004;80:1650-1657.
  2. Balk E, Chung M, Lichtenstein A, et al. Effects of omega-3 fatty acids on cardiovascular risk factors and intermediate markers of cardiovascular disease: Agency for Healthcare Research and Quality; March 2004.
  3. Wang C, Chung M, Lichtenstein A, et al. Effects of omega-3 fatty acids on cardiovascular disease: Agency for Healthcare Research and Quality; March 2004.
  4. Anderson GJ, Connor WE, Corliss JD. Docosahexaenoic acid is the preferred dietary n-3 fatty acid for the development of the brain and retina. Pediatr Res. 1990;27:89-97.
  5. Connor WE, Neuringer M, Lin DS. Dietary effects on brain fatty acid composition: the reversibility of n-3 fatty acid deficiency and turnover of docosahexaenoic acid in the brain, erythrocytes, and plasma of rhesus monkeys. J Lipid Res. 1990;31:237-247.
  6. Conquer JA, Tierney MC, Zecevic J, Bettger WJ, Fisher RH. Fatty acid analysis of blood plasma of patients with Alzheimer's disease, other types of dementia, and cognitive impairment. Lipids. 2000;35:1305-1312.
  7. Kalmijn S, Launer LJ, Ott A, Witteman JC, Hofman A, Breteler MM. Dietary fat intake and the risk of incident dementia in the Rotterdam Study. Ann Neurol. 1997;42:776-782.
  8. Barberger-Gateau P, Letenneur L, Deschamps V, Peres K, Dartigues JF, Renaud S. Fish, meat, and risk of dementia: cohort study. Bmj. 2002;325:932-933.
  9. Morris MC, Evans DA, Bienias JL, et al. Consumption of fish and n-3 fatty acids and risk of incident Alzheimer disease. Arch Neurol. 2003;60:940-946.
  10. Guallar E, Sanz-Gallardo MI, van't Veer P, et al. Mercury, fish oils, and the risk of myocardial infarction. N Engl J Med. 2002;347:1747-1754.
  11. Yoshizawa K, Rimm EB, Morris JS, et al. Mercury and the risk of coronary heart disease in men. N Engl J Med. 2002;347:1755-1760.

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