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Why fish is essential for health

What does a coldwater fish like tuna have in common with human breastfeeding? The answer lies in a fatty acid that goes by the acronym DHA. It is an old wives’ tale that those who eat fish are smarter but, as it turns out, some of those old wives knew what they were talking about. Recent research has highlighted the true benefit of fish for the brain. This fishy tale is highly relevant if you are a parent but also has implications if you are concerned with depression and the maintenance of your mental faculties as you age.

Vital DHA

As a six-year-old albacore tuna edges its muscular, tapered body through the deep, cold ocean water, its thought process might well be along the lines of “Swim — seaweed — swim — algae — swim — squid — swim — eat — swim — killer whale! — swim, swim, swim…” and so it goes. Hardly the lifestyle or mental ability of the tutor you would imagine to maximise your child’s learning abilities! Yet, within tuna lies an essential component to your baby’s neurological development, intellectual achievement, behaviour and mental capacities as she/he ages.

Coldwater fish such as tuna and also mackerel, salmon, herring, sardine, black cod and anchovy have a plentiful supply of oil, probably as insulation against their cold habitat. It’s no exaggeration that this oil is more precious than its petroleum counterpart sucked from pockets within the earth’s crust, for within this fish oil lies a component that is absolutely essential for the development of the human brain.

In fact, this substance is so vital to the growth of the foetus that if there is not enough of it in the mother’s diet for her to pass on to the foetus, the mother’s own brain might be robbed by the body to make sure the developing baby gets what it needs.

The human body can manufacture this substance but it’s a difficult and slow process. Even the tuna and other fish don’t make it but absorb it from the microalgae they consume in the course of their deepwater journey. The substance is DHA and it is literally ‘mother’s milk’ to your baby’s brain and your own mental health.

DHA biography

An important first point to make is that the substance at issue here is DHA and not DHEA. DHEA (dihydroepiandrosterone) is a steroid hormone made by the human adrenal glands and is quite a popular supplement in the USA, used for its reputed enlivening and anti-ageing properties. However, it is not the substance under discussion here.

What differentiates a saturated from an unsaturated fat is that unsaturated fatty acids contain at least one double bond in their chain.

DHA (docosahexaenoic acid) is an omega-3 long chain polyunsaturated fatty acid (LCP). The health benefits of LCPs have long been recognised but it remains a fact that the average diet in developed countries does not feature as much of them as is optimal. To understand the benefits of LCPs it’s necessary to understand the structure of these oils.

All oils are composed of sub-units called fatty acids that are assembled in a chain-like fashion. What differentiates a saturated from an unsaturated fat is that unsaturated fatty acids contain at least one double bond in their chain. The absence of double bonds makes the fat ‘saturated’, with the characteristic of being thick and hard at room temperature, like butter and other animal fat. Unsaturated fats, however, are thin and viscous at room temperature, and the more double bonds they contain, the more fluid the oil.

DHA is a ‘super-unsaturated’ oil in that it contains six double bonds; it’s this quality that partly lends to its many health benefits. DHA has been found to be highly concentrated in the human brain and the retina of the eye. It’s known that DHA is essential for normal vision and the normal development of the nervous system in infants. Clinical trials support the use of DHA in premature infants to encourage better brain functioning. Beyond this, the effects of DHA on the nervous system might extend into adult life.

Baby’s brain and mother’s milk

In the last trimester (three months) of pregnancy the infant brain undergoes an astonishing growth spurt. It is in this time that the cerebral cortex, the thinking portion of the brain, develops. The dramatic growth of the brain continues throughout the first year of life. Research indicates that DHA is a critical nutrient for this growth, as was stated in a paper published in the Lancet (1995) by Makrides et al: “DHA seems to be an essential nutrient for the optimal neural maturation of term infants…” DHA is the most abundant structural fat in the brain and the retina of the eye. Brain tissue is about 60 per cent structural fat; of this, 25 per cent is DHA. Additionally, DHA comprises about 60 per cent of the rod outer segments in the retina, which has important impacts on vision.

Despite the importance of DHA, the human foetus cannot produce it and depends on receiving an adequate supply from the mother’s blood passed through the placenta. After leaving the womb the baby still requires a lot of DHA and finds it supplied through the mother’s milk. It’s quite well established that breastfed babies tend to be brighter than those fed on formula.

Research findings

The University of Milan reports that infants whose formula contains long chain fatty acids (especially DHA) have better brain development than children who don’t receive DHA in their formula and recommends that mothers should breastfeed if possible. Another study compared infants who had been breastfed to those who had been formula-fed and also to those who had been fed formula milk supplemented with a blend of fish oils and evening primrose oil. The results showed that breastfed babies had better reactions than formula-fed babies, but the babies fed on supplemented formula matched the performance of breastfed infants.

A recent study published in the journal Developmental Medicine and Child Neurology (v42, p174) measured the mental development of a group of babies at 18 months, using a scale called the Mental Development Index (MDI). On this test an average score is 100, and breastfed infants typically score five points higher than bottle-fed babies. In this research, infants fed on a formula supplemented with DHA and arachidonic acid (another fatty acid) averaged a score of 105; those fed on formula plus DHA averaged a reading of 102; and those on formula alone averaged a score of 98.

The clear message is that DHA is critical to the mental development of your baby.

The clear message is that DHA is critical to the mental development of your baby. It’s also true that the benefits of receiving this supply of DHA while in the womb and in the first few weeks of life are critical and have an ongoing impact. It appears that the period up to 16 weeks after birth is when DHA is necessary, but beyond this point it is not so critical.

One study followed the development of infants born prematurely over an eight-year period and found that those who had consumed breastmilk in the early weeks of life had a significantly higher IQ than those who had received no maternal milk. The dubious nature of IQ measuring aside, the developmental advantages of early access to DHA seem clear. So the key question is how to give it to your child.

Where do you get DHA?

Optimally, you can provide your baby with the DHA it needs via breastmilk and the ideal is to breastfeed for four to six months at least. Even forgetting DHA for a moment, the range of physiological benefits of breastfeeding for the baby, and probably for the mother, too, can never be matched by formula. The amount of DHA a mother will have in her breastmilk is directly related to the amount she consumes in her diet.

DHA can be obtained from sources such as eggs and organ meats. However, for the increasing number of people who seek to limit their intake of these foods for health and philosophical reasons, the best source is fish oil. Of the fish oils mentioned already, tuna has the highest DHA content. Many standard fish oil supplements are salmon oil and contain DHA but not at the same levels as tuna. Cod liver oil contains DHA but also contains vitamin A, which needs to be taken with caution during pregnancy.

DHA needs to be consumed in the diet, as, although the body can make DHA, it’s very difficult for it to do so. This is shown by a study in which subjects were given a flaxseed supplement for four weeks. Flaxseed (also known as linseed) contains alpha-linolenic acid (ALA), from which the body can make DHA. After the four weeks these subjects did not have raised blood levels of DHA, in contrast to people supplementing with fish oil who did have a raised blood DHA. This is because the body has an enzyme called delta-6-desaturase, which is necessary for the conversion of ALA to DHA. Unfortunately, that enzyme is in great physiological demand and is not always available, making the body’s manufacture of DHA slow and inefficient.

It’s important, then, for pregnant women and nursing mothers to consume adequate DHA in their diets to pass on to their babies. A dose of 400mg of DHA daily would be adequate for most pregnant or nursing mothers. If, for some reason, you are unable to breastfeed, the option of supplementation arises.

In Europe DHA has been used in infant formulae since the mid-1990s. The Food and Drug Administration of the USA plans to revisit in 2003 the subject of adding DHA to infant milk formula. In Australia you will have to do some searching of your own. Simply adding fish oil to your formula might not be the answer, as your baby might not require the other substances contained therein and could have difficulty dealing with them. Depending on the size and particular needs of your baby, speak to a clinic sister or your local pharmacist to find a formula to meet your requirements.

ADD and aggression

It is already clear that DHA deprivation can have long-term effects into a child’s later life, but there are also indications that supplementing with DHA can have definite benefits in reducing aggressive behaviour and in treating the troublesome condition known as Attention Deficit Disorder (ADD).

ADD is the term currently used to describe what has been variously labelled in the past as ‘hyperactivity’ or ‘learning disability’. Features of the condition include emotional instability, short attention span, hyperactivity, disorders of memory and learning and, of course, parents who are driven to distraction. There is substantial evidence showing that children who suffer this condition have low blood levels of DHA and other LCPs. While ADD is a complex condition and should only be treated in conjunction with a health practitioner, there is evidence to suggest that DHA and other LCPs can be helpful. In modulating other behavioural states DHA is certainly of benefit.

Boys who throw temper tantrums and who have sleep problems have been shown to have low omega-3 LCP levels. It might be an idea to include some omega-3 oils in your meals at exam time, since DHA supplementation has been effective in preventing aggression at times of mental stress.

In general, then, this fatty acid, which is a structural component of the brain’s grey matter, the retina of the eye and the fats that sheathe the nerves, seems essential for balanced mental function and might therefore be useful in cases of depression.

Depression — the DHA link

The need for adults to have adequate DHA is highlighted by the link between disturbed fatty acid metabolism and the conditions of depression and bipolar disorder (formerly known as manic depression). These two conditions are quite common in the developed world. A recent study has shown that approximately 30 per cent of patients do not respond to drugs commonly prescribed for these conditions. There is evidence to show that in bipolar disorder there is disturbed fatty acid metabolism, and depression might be the result of reduced levels of omega-6 and omega-3 fatty acids such as DHA and eicosapentaenoic acid (EPA). Both of these oils have been found effective in trials on bipolar disorder, where there was no response to other treatment.

Long-term studies indicate that as consumption of omega-3 LCPs such as DHA has decreased over the past century, so has the incidence of depression increased. Such a link does not prove a cause-and-effect relationship but other evidence does support the use of these fatty acids in certain instances of depression. One such study conducted at the Brigham Women’s Hospital in Boston, USA, found that patients with manic depression experienced relief from their symptoms with large doses of fish oil.

Seeing the benefits

It’s worth paying a final moment’s attention to the role of DHA in vision. In the human retina there are two receptors for light that are central to the visual process: the cones are responsible for colour perception; the rods are required for perception of light and dark and, therefore, night vision.

Both rods and cones are lined with an insulating layer of fatty acids, primarily DHA. Rhodopsion, the pigment required for night vision, is surrounded by about 60 phospholipid molecules, most of which are composed of DHA. It’s not surprising, then, that DHA supplementation has been shown to improve night vision and that infants given a formula that includes omega-3 LCPs exhibit visual improvement when compared with infants given standard formula.

A word on supplementations

If you do decide to take a DHA-containing fish oil supplement it’s important to consume more vitamin E. This is because fatty acids are open to attack from free radicals and the antioxidant vitamin E must protect the fats from destruction. Indeed, simply consuming a lot more fatty acids, thus calling vitamin E into action, can cause a vitamin E deficiency. Many fish oil supplements come with vitamin E included for this reason, but you may want to take some additional vitamin E to be sure.

Terry Robson

Terry Robson

Terry Robson is the Editor-in-Chief of WellBeing and the Editor of EatWell.

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