CHUKWUMA MUANYA reports that people who consume dark-flesh fish, such as cod, salmon or tuna, at least once a week have a 15 per cent lower risk of cataracts than did those eating fish less frequently.

FRESH evidence has emerged on the benefits of consuming dark flesh oily fish. Before now, eating dark flesh oily fish such as salmon and cod, which are rich in omega-3 fatty acids, has been shown to improve brain function and reduce the risk of developing heart diseases and arthritis.

However, recent studies link mayonnaise, creamy salad dressings, cheese, beef, pork, and lamb, as well as certain vegetable oils, to an elevated risk of age-related cataracts. One of those studies, however, also suggests that oily fish, the type with dark flesh, hold cataracts at bay.

Age-related cataracts are the leading cause of blindness. Indeed, cataract surgery is the most frequent eye-related surgical procedure performed in Nigeria.

These were disclosed to The Guardian in an exclusive interview with the Secretary, International Society for the Study of Fatty Acids and Lipids, Dr Ray Rice, at a seminar held by Seven Seas Limited (a world leader in Nutritional Research and the production of Fish Based Consumer Healthcare Products) in Lagos. These were also corroborated by Professor H. Olusanya Adeyemi-Doro, head, Trauma and Hand Rehabilitation Unit, Department of Surgery, Lagos University Teaching Hospital (LUTH), Idi-Araba.

Rice said: " The bottom-line is that if you do not eat fish at least twice a week, you are not getting enough omega-3 and your body will be likely to suffer from age-related cataracts, heart disease, arthritis, depression, poor mental development and mental disorders. The white coloured flesh oily fish does not have much omega-3, but the dark coloured flesh fish has high omega-3 content. If you ate that twice a week, then you will be quite fine.

"But if you eat walnut, flaxseed, linseed and white coloured flesh fish, that means you will not be getting enough omega-3 and the chances is that you will be getting too much of omega-6. Having part of these two, omega-3 and omega-6, in the body will not be ideal and may predispose the body to some health risks that may not make themselves apparent till about 30 to 40 years latter. Down the line you will be more likely to developing age-related cataracts, irregular rhythm, heart beats, more risk of heart disease, the joints will be susceptible to wear and tear. In any way, if you have enough omega-3 intake, that will not be the case."

Rice argued it is better to go for cod liver oil supplements because the form present in walnuts, flaxseed or linseed oil and small amounts in green vegetables is not enough, and is not particularly useful to the body; it has to be converted into a different form.

He insisted that dark coloured flesh oily fish is the best source of omega-3. " We should get it from fish than from supplements. But there are many people who do not have access to fish, maybe fresh fish, some people do not like fish, some people are allergic to it, they do not know how to cook it, they do not like the smell, all sort of reasons. So it is important that we have a good reliable source of omega 3 available in the form of cod liver oil," Rice said.

Cod liver oil comes from the liver of cod. Cod is a big fish found in arctic regions. Cod is unique because it stores its oil in the liver, which is 10 per cent the weight.

Rice continued: "Traditionally, cod liver oil has been valued because of the Vitamin A and Vitamin D content which is barely unique, because it has such high concentration of these nutrients, and it is especially valued in Africa where their deficiency is a major problem. But in the past 30 to 40 years, we have found out more about the composition of the oil. Particularly, one of the components the oil is made from, the omega-3 polyunsaturates is unique because there are no other components of our diet that contains such large amounts than fish. The human body must have a certain amount of these polyunsaturates to remain healthy.

"There are two families of what we call essential fatty acids, and omega-3 family is one of them and omega-6 is the other. If humans do not have small amounts of these nutrients in their diets on regular basis, then their health deteriorates and that is really the basic message. There is a wide range of positive effects when the omega-3 intake is increased by taking cod liver oil or fish, or some other means. Each and every area of the body uses the omega-3 to enable it to function the way that God intended."

Indeed, a team of researchers from Boston, United States, in their first study of women participating in a nearly-30-year-old diet-and-health study, published in the American Journal of Clinical Nutrition link the primary fat in corn oil, linoleic acid, to incipient cataracts, called opacities, in the lenses of the women's eyes. In this study, this single fat accounted, on average, for roughly five per cent of calories consumed each day, and more than 85 per cent of polyunsaturated-fat intake.

Paul F. Jacques, director of nutritional epidemiology for the Agriculture Department's Jean Mayer Human Nutrition Research Centre on Ageing at Tufts University, United States, notes that

lens opacities are "a sensitive marker for the development of cataracts" but does not initially cause vision loss.

The second study, also by Jacques' team, included women who had undergone surgery for removal of cataracts. Compared with women their age who never had such a procedure, these women were much less likely to have eaten omega-3 fatty acids, the type found in many fish oils. In this study, eating vegetable oils did not appear to be linked with cataracts, but eating mayonnaise and salad dressings did.

The studies appear slightly contradictory, acknowledges Jacques. However, he adds, it might be that one type of fat is more likely to affect early stages of cataract susceptibility and the other has its most notable impact in the latter stages of cataract development. In any case, the findings are consistent with earlier work suggesting that fat consumption can affect a person's vulnerability to cataracts.

Reacting to the study, a biologist at the University of Lagos, Akoka, Professor Peter Odeigah said: "That makes sense because fatty substances affect the flexibility and permeability of cell membranes throughout the body. Cataracts are associated with changes in lens-membrane structure and function and, thus, could be affected by dietary fats."

For their initial study, the Boston researchers invited local women, ages 53 to 73, to have their eyes examined. All were participants in the ongoing Nurses Health Study based at Brigham and Women's Hospital in Boston and begun in 1976.

None of the 440 volunteers had a previous diagnosis of cataracts or of a disease such as diabetes that would have put them at high risk of cataracts. Roughly 45 per cent of the women had clear lenses. Of the remainder, most had the first signs of cataracts in multiple types of lens tissue. Sixty per cent of the women with opacities were developing a type that affects the lens' core, or nuclear region.

The researchers then evaluated the typical intake of various fats by these women, based on dietary questionnaires they had filled out at regular intervals since 1980. The women described how often they ate each of some 130 foods, and how much. Previous tests of this survey indicated that it yields accurate data on people' consumption of more than 90 per cent of 70 key nutrients, including many fats.

The scientists report that women whose diets were richest in polyunsaturated fats were significantly more likely to have incipient nuclear cataracts, and those whose diets were lowest in this fat were least likely. A higher risk of early nuclear cataracts was also associated with diets high in vegetable oils and trans fats. Earlier studies in rodents had suggested that diets high in corn oil cut an animal's risk of cataracts.

No increased cataract risk was associated with intake of animal fats, which include saturated fats. Neither of the two other classes of incipient cataracts-opacities affecting the edges or back of the lens-showed a link to dietary fats of any type.

When the researchers focused on the women's consumption of various types of polyunsaturated fats, cataract risk appeared to be most associated with two fatty acids: linoleic and linolenic.

Linoleic acid is the major constituent of safflower, sunflower, corn, soybean, and cottonseed oils. Although linolenic acid is found in many plant oils, its highest concentrations tend to be in flax, soy, walnuts, and canola. Most dietary trans fats have been engineered by chemically altering such polyunsaturates to make them solid or semisolid at room temperature-ideal for margarines and shortenings.

The researchers urge caution before indicting linolenic acid for causing cataracts. First, two previous studies by other researchers found almost no linolenic in the eye's lens. Also, oils rich in this fat are smaller contributors to the U.S. diet than is linoleic-dominated corn oil. Moreover, linolenic acid occurs in many of the same sources as linolenic acid does, just in smaller quantities, making its cataract contribution hard to distinguish. Finally, the body tends to convert some of its linolenic into two long-chain omega-3 fats abundant in many fish oils: Docosahexaenoic and eicosapentaenoic acids, better known as DHA and EPA, respectively.

In this study, the only major foods that actually stood out as apparent risk factors were mayonnaise and creamy salad dressings. These condiments tend to be rich in linolenic acid.

The second study by Jacques and his team also mined data from the Nurses Health Study, but in this case, dietary information supplied by some 71,000 women between 1984 and 2000. To be included for this analysis, a woman could not have had a cataract, cancer, or diabetes when the study began in 1976. After eliminating individuals with certain other potentially confounding conditions, the researchers found that 4,196 women in the group had cataracts diagnosed after age 45 and then had surgery. Roughly 60 per cent of these cases involved nuclear cataracts.

As in the first study, Jacques' group assessed possible dietary contributions to cataracts by comparing the participants' typical intake of various types of fats.

One finding stood out, Jacques notes: Women who developed cataracts were far less likely to be big fish eaters.

Indeed, women who consumed dark-meat fish, such as salmon or tuna, at least once a week had a 15 per cent lower risk of cataracts than did women eating fish less frequently. Dark-meat fish are the ones that tend to be especially rich in DHA and EPA.

Among foods associated with an increased risk of cataracts were mayonnaise, creamy salad dressings, cheese, beef, pork, and lamb.

Jacques says his team wants to see if it can verify its findings in a different population. It also wants to go a step beyond analysing data on what women say they eat to actually measuring fatty acids in people's blood to see whether their abundance there correlates with a risk of cataracts.

According to Rice, if the body does not have omega-3s it does not function quite so well. " It does not stop working but it does not work quite as well. It is like if you put wrong engine oil in your car it will still get you to the place you want to go but it will make a lot of smoke and noise. That is what happens to the human body when it does not have enough omega-3. It does work but it does not work as well, and it will be more susceptible to a number of conditions such as depression.

"Depression is interesting because the human brain is a major area where omega-3 polyunsaturates are located. Like 10 per cent of the brain is omega-3. If you do not have enough omega 3 in the diet, the amount in the brain is not in the right level and the brain does not work as it is supposed to, you are more likely to be aggressive, to have difficulty in paying attention. Children have a phenomenal rates in the United Kingdom what we call Attention Deficient Hyperactivity Disorder (ADHD), they do not pay attention to school, they are rude to their parents and teachers, they do all sort of things, they cannot concentrate. This is one of the effects that we are finding that when you give children small amounts of cod liver oil and their behaviour improves, their work performance in school improves, they do not fall sick so much, so they do not miss too much schooling," he said.

Rice recommends cod liver oil to all age groups. " It is for all age groups because the human body needs a certain amount of omega 3 and if it does not get it at, different effects will become apparent at different ages. It has individual variations. So for the young it is important for brain development.

"Development of the baby's brain takes place during the last three months in the womb and the next 12 months after birth. When the brain is formed, no other changes takes place. It does not get bigger. The number of brain cells formed stops after one year of age. No more new cells are formed. They get bigger and they make connections with each other. But no new brain cells are formed after that one-year. To form those brain cells and make them bigger and better connect with each other, a child needs certain amounts of omega 3 in its diets.

"If a child is being breastfed it will get that from the mothers breast milk because it does contain omega 3 and omega 6. If a child is being bottle-fed, the bottle formular may not have these things in it. Some of them do and some of them do not. Studies have shown that if a baby has good supply of omega 3, its eyesight develops more rapidly. It is more quickly able to recognise its mother, bonded to the mother and also brain development activity occurs slightly faster.

"Omega 3 is one of the building blocks cod liver oil is made up of, and fish and fish oil are the only things in our diet that contains significant amounts.

"Cod liver oil has small effect on the good cholesterol, High Density Lipo-protein (HDL). It raises it to about 10 per cent. It does not have much effect on the bad cholesterol, Low Density Lipo-protein (LDL). It does have a good effect on triglycerides, which is another type of fat found in the blood and which is linked to increased risk of heart disease. Cod liver oil brings down the triglycerides level which makes the blood clot less likely and also reduces risk of heart disease and raises the HDL cholesterol to about 10 per cent."

According to the International Business Manager, Seven Seas Limited, Mr Alan Smith, Seven Seas products are recommended and prescribed as first choice for the increasing number of treatment areas. He said there are two basic variations of the preparations of cod liver oil by Seven Seas. "We have high strength Vitamin A and D, which we export to those countries with high Vitamin A deficiency. We also have much larger range being developed."