Last week, researchers reported that diets rich in fish-borne omega-3s may reduce the risk of age-related macular degeneration (AMD) by about 40 percent.

At the same time, high intake of the omega-6 fatty acids vastly overabundant in American diets were associated with increased risk of AMD.
 

These findings highlight the dangers of the woefully imbalanced American diet, which is much too low in omega-3s and much too high in omega-6s: the two families of dietary fatty acids whose previously overlooked interactions and health effects have finally become the focus of extensive research.
 

The results come from a study involving 4,519 older people, which found a strong association between fish-rich diets and lower risk of AMD.

(Note: In a companion study, the vitamin D abundant in wild salmon was found to exert complementary preventive impacts on AMD. See "Vitamin D Adds Eye Health to Roster of Recent Accolades", in this issue of "Vital Choices".)

AMD is the leading cause of blindness in Americans aged 55 and older, and of the 30,000,000 people over age 65 in the US in 1990, almost one in three show evidence of the eye disease. The number of Americans over age 65 will double by the year 2030, so researchers have sought to reveal any foods that might help prevent the vision-crippling condition.

AMD comes in two forms: early or "dry" stages, and subsequent "wet" stages. The wet forms are named for the under-retina overgrowth of blood vessels that characterize this type of AMD. Although it afflicts less than 10 percent of patients, wet AMD causes 85 percent of severe AMD-related vision loss.

The majority of wet AMD cases get little help from the leading therapy, called laser photocoagulation. But in recent years, this procedure's efficacy has been greatly enhanced by injecting patients with a drug called verteporfin before the laser treatment is applied. (While results vary, this writer's 70-something stepmother underwent the drug-laser AMD treatment recently, with very substantial success.)

The new findings support the AMD-preventive potential of inflammation-moderating omega-3s, and they also extend to eyes the health risks associated with the excessive intake of inflammation-fueling omega-6 fatty acids characteristic of the average American's diet.

Omega-6 fatty acids compete with omega-3s for space in the membranes of eye cells (and all body cells). Excessive dietary intake of omega-6s is known to promote cancer growth, and it now appears that Americans' typical omega-6 overload may be a threat to aging eyes as well, probably because of their pro-inflammatory effects.

Omega-6s abound in standard, grain-fed meats and poultry and they predominate in the vegetable oils used most commonly for home cooking and in packaged and restaurant foods (corn, safflower, soy, canola, sunflower, and cottonseed).

Let's take a closer look at the enlightening details of the new study.

Americans' low omega-3/omega-6 diet ratio poses long-term vision risks

The new findings flow from analysis of data from the Age-Related Eye Disease Study (AREDS), conducted under the auspices of the National Eye Institute (NEI).

AREDS involved researchers at universities and clinics in nine states, who enrolled 4,757 subjects, surveyed the participants about their diets and lifestyles, and gave them detailed eye exams.

Some novel findings in young men add to the evidence that higher omega-3 intake helps build stronger bones.

Researchers at Sweden's Umeå University report that young men with higher blood levels of omega-3s have denser, stronger bones (Hogstrom M et al 2007).  

Surprisingly, no one had ever examined the association between body levels of dietary fatty acids and standard markers of bone strength such as bone mineral density or BMD.

In previous studies, researchers relied on food intake questionnaires to estimate people's intake of fatty acids relative to their bone density: a factor associated with bone strength, though not always synonymous with reduced fracture risk.

What the study found

A team led by Magnus Högström, PhD recruited 78 healthy young men (average age of 16.7 years) from high schools and sports clubs, measured total body bone mineral density (BMD), and took blood samples to measure their levels of omega-3 and omega-6 fatty acids.

About eight years later, Dr. Högström's group found that the young men with the highest tissue levels of omega-3s had the best (highest) total-body BMD and spinal BMD, and the greatest growth in BMD between the ages of 16 and 22.

Of the two omega-3s - DHA and EPA - levels of DHA had the closest associations with these two measures.

As Chaim Vanek, M.D. and William Connor, M.D. of Oregon Health & Science University said in an accompanying editorial, "The study by Högström et al. nicely adds to a growing body of evidence that n-3 fatty acids are also beneficial to bone health." (Vanek C, Connor WE 2007)

Drs. Vanek and Connor hypothesized that the apparent benefits might relate to the opposite effects of omega-3 and omega-6 fatty acids with regard to cell receptors for a genetic switch called PPAR-gamma, excessive activation of whose cell receptors is associated with lower bone mass:

• Omega-6 fatty acids, in excess, weaken bone because they activate PPAR-gamma cell receptors in bone marrow. Americans consume far too many omega-6s.
• Omega-3 fatty acids conserve bone density, because they do not activate PPAR-gamma cell receptors in bone marrow.

Although Drs. Vanek and Connor say that omega-3s do not activate PPAR-gamma cell receptors in bone marrow, diabetes studies indicate that marine omega-3s do activate them.

   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.)

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.

*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. 

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.

Recent headlines from Holland trumpeted the apparent ability of folic acid (folate) - one of the B vitamins - to slow progress toward senility. Folate is concentrated in green leafy vegetables, beans, lentils, hazelnuts, and liver.

But most media reports overlooked a simultaneous announcement by researchers from Boston's Tufts University, which suggest that taking folate alone could increase one's age-related slide toward senility.

Dietary folate can also accelerate progress toward senility and dementia unless people also consume adequate amounts of vitamin B-12, which, supplements aside, is abundant only in animal foods and fermented soy beans (tempeh).

The Tufts researchers suggest that public health officials consider requiring food makers to fortify flour with B-12, because folic acid is already added to flour to help mothers prevent neural tube defects in their developing fetuses (Morris MS et al 2007), this creating the possibility of a senility-promoting imbalance between these B vitamins.

Therefore, as the Dutch group noted, the effect of taking supplemental folic acid might be less in the US, where fortification of flour with folic acid is mandatory, and people have lower blood homocysteine levels.

They also note that -- unlike many nursing home residents -- all of the participants had sufficient levels of vitamin B12, deficiency of which can cause anemia and dementia in elderly people.

They noted that the study involved people with slightly raised levels of the amino acid homocysteine, so the results might not be as clearly beneficial in people with lower homocysteine levels.

Folate benefits brains only when B-12 is present

The well-designed Dutch trial (randomized, double-blind, placebo-controlled) was intended to see whether supplemental folic acid would enhance mental performance in people with adequate levels of vitamin B-12 but slightly elevated blood levels of homocysteine (Durga J, van Boxtel MP, et al 2007).

Elevated homocysteine may promote cardiovascular disease, and people with slightly raised levels run an increased risk of or age-related cognitive decline (ARCD): the medical term for geriatric senility.

Homocysteine in the blood is either metabolized (broken down) through a mechanism that uses vitamin B6, or can be converted into harmless methionine through one of two separate routes that require either folic acid or vitamin B12.

The Dutch researchers recruited 818 men and women between the ages of 50 and 70, with slightly elevated blood homocysteine levels (13 micromoles per liter or more) and healthy vitamin B12 levels (at least 200 picomoles per liter).

The participants were randomly assigned to take either 800 micrograms of supplemental folic acid - which is double the US RDA -- or a placebo for three years.

Their cognitive function was assessed at the beginning and end using a battery of tests.

The researchers found that folic acid supplementation gave subjects the memory performance of someone 4.7 years younger, the reaction time of someone 1.7 years younger, the information processing speed of someone 2.1 years younger, and the "global cognitive function" of someone 1.5 years younger.

They also reported that the "delayed recall" performance of the folic acid group compared favorably to the performance of someone 6.9 years younger. (Delayed recall means remembering information after a delay; usually about ten minutes.))

As the authors wrote, "We have shown that 3-year folic acid supplementation improves performance on tests that measure information processing speed and memory, domains that are known to decline with age."

Folate may reduce hearing loss

The same Dutch team also looked at hearing loss among study participants.

At the outset of the three-year study, they measured the participants' average threshold for hearing in the low and high frequency ranges.

By the end of the study the hearing thresholds had increased among members of the folic acid and placebo groups. In other words, noises had to be louder before the participants heard it.

However, the undesirable increase in hearing thresholds in the low frequency range was substantially smaller in the folate group than in the placebo group (1.0 decibels versus a 1.7 decibels increase).

Ankylosing spondylitis (ank-kih-low-sing spon-dill-eye-tiss) or AS is an autoimmune, rheumatic-type disease that affects some 400,000 adult Americans: about as many as have rheumatoid arthritis. The vast majority (90-95 percent) of AS patients have a genetic marker (HLA-B27) that's far less common in the general population.

Unlike most autoimmune rheumatic diseases (e.g., rheumatoid arthritis, lupus and scleroderma) three-quarters of AS patients are men.

AS is characterized by inflammation of the spinal joints (vertebrae) that can lead to severe, chronic pain and discomfort.

The symptoms of AS - for which there is no known cure -- often appear by age 30, and can include the following:

• Dull or tender pain in the lower back and hip joints (sacroiliac), rib joints, neck back or shoulders.
• Low-grade inflammation.
• General fatigue, fever, and stiffness.
• Pain where tendons attach to bone (ankles, buttocks, knees and shoulders).
• Eye inflammation.

In the most advanced cases, inflammation can prompt new bone formation that forces the spine to fuse in a fixed posture.

Researchers at Sweden's Gallivare Hospital, led by Dr. Bjorn Sundstrom, recruited 18 AS patients from polar and sub-

polar regions of Sweden where AS and its genetic marker are unusually common.

Interestingly, Inuits (AKA Eskimos; see "Native names" sidebar) who have the genetic marker for high risk of developing AS - and who, unlike white residents of North Sweden, consume lots of omega-3s from fish and marine mammals -- rarely develop the disease.

The Swedes divided the participants into two groups of nine patients each, with one group taking lower daily doses of omega-3s (1.95 grams EPA + DHA) and the other taking fairly high doses (4.55 grams EPA + DHA). The study lasted for 21 weeks.

As Dr. Sundstrom and his colleagues reported, "The patients in the high-dose group exhibited a significant decrease in disease activity according to the Bath Ankylosing Disease Activity Index, which was not seen in the low-dose group … Omega-3 fatty acids in adequate doses may have the capacity to decrease the disease activity of AS."