DHA Introduction :
Docosahexaenoic acid (DHA) is an
omega–3 fatty acid which is an essential fatty acid. Essential fatty acids cannot be synthesized in the body. They are also called polyunsaturated fatty acid (PUFA). These PUFA must be obtained from dietary food. There are 2 types of PUFA – omega 6 and omega 3. Omega 3 fatty acids are also known as Long Chain polyunsaturated fatty acids (LC PUFA’s). The most important omega 6 (n-6) fatty acid is arachidonic acid (ARA) that is formed from linoleic acid (LA) while most important omega 3 (n-3) fatty acid is DHA which is formed from alpha – linolenic acid (ALA ) (1).
Throughout most of life, there is a very limited metabolic capacity to convert ALA to DHA (2). Essential fatty acids are structural components of all tissues and are indispensable for cell membrane synthesis; the brain, retina and others neural tissues are particularly rich in long chain PUFA. These fatty acids serve as specific precursors for eicosanoids, which regulate numerous cell and organ functions (3). The most abundant brain PUFA are DHA (n-3); arachidonic acid (n-6) and adrenic acid (n-6) (4) and DHA is most abundant in the outer rod photoreceptors in the eye.
DHA is an omega 3 PUFA which has very limited synthesis in the body. In the human body, DHA is derived from eicosapentaenoic acid (EPA) via docosapentaenoic acid (DPA) as an intermediate by desaturase enzyme and beta oxidation in peroxisomes (5). During early life, there is limited metabolic capacity to convert ALA to DHA. Thus in fetal life, infancy and early childhood, DHA should be acquired from dietary sources to maintain optimal health (6).
Intake of DHA in children: Eicosapentaenoic acid (EPA) and DHA intake is often low in 2-12 years old children relative to intake in breast fed infants and adult intake. It has been found that large proportions of children have low levels of intake of n-3 omega fatty acids with >97% of all groups consuming less than 1% energy from this fats due to poor intake of EPA & DHA. (3)
Consumption of healthy diets that contribute with adequate amounts of fat and fatty acids is needed to children. (3) Dietary intakes in childhood should support future adult health such as prevention of metabolic disorders & cardiovascular disease, support immune function and maintain healthy reproductive system (4).
DHA is predominant in fish and seafood and consumption of these foods in Indian children is virtually lacking. In vegetarians the predominant polyunsaturated fatty acid is linolenic acid (LA) - an omega 6 fatty acid. Alpha linolenic acid (ALA) which is an omega 3 fatty acid is not so abundant in vegetarian diets. (5) ALA is a precursor of EPA and DHA. The ideal ratio of LA to ALA should be 3:1 in the diet, however most diets have a ratio of 10:1 or 15:1. (5) Under these circumstances, omega 6 fatty acids inhibit the conversion pathway of omega 3 fatty acids. Thus decreasing LA content has been found to increase the ALA conversion to EPA and DHA.
Sources of DHA :
Fish oils are rich in DHA. Most of the DHA in fish and other organisms originate from microalgae. ALA is present in vegetable oils such as flaxseed or linseed oil, rapeseed or canola oil, peanut oil, olive oil, soya oil, walnut oil, green leafy vegetables, fenugreek seeds, kidney beans and dry fruits (7). DHA is also manufactured from microalgae in vegetarian form (1) for commercial use.
The DHA content in various foods is depicted in Table 1:
Table 1: Dietary sources of DHA
|Grams of omega – 3 fatty acid|
|(per 3 oz serving)|
|0.21 – 1.1|
|1.1 – 1.9|
|0.15 – 0.24|
|0.22 – 0.3|
|0.60 – 1.12|
» Mahi mahi
» Orange Roughy
» Red snapper
» Sword fish
» Tile fish
» King mackerel
|Percentage of omega – 3 in seed oil|
|55(18% of omega-3 in the whole food|
|19 (8.7% of omega 3 in the whole food)|
Daily requirement of DHA:
While exact dose of DHA to be consumed is not known, the following are recommended:
Pregnant and Nursing women: A workshop sponsored by the National Institutes of Health and International Society for the study of fatty acids and lipids (NIH/ISSFAL) recommended an intake of 300mg/day of DHA
Children and Healthy Adults" NIH/ISSFAL have recommended an intake of 220 mg/day of DHA.
Body stores of DHA :
Over the first 6 months of life, DHA accumulates at about 10 mg/d in the whole body of breast–fed infants with 48% of that amount appearing in the brain. To achieve that rate of accumulation, breast–fed infants need to consume a minimum of 20 mg DHA/d. Virtually all breast milk provides a DHA intake of at least 60 mg/d though it may be variable. Thus a store of about 1050 mg of DHA in body fat at term birth is present (8).
DHA (food) concentrations in breast milk range from 0.07% - >1.0% of total fatty acids with a mean of 0.34% depending on maternal DHA intake (1). A working group from the ISSFAL (International Society for the study of Fatty Acids & Lipids) has recommended 300 mg/day of DHA for pregnant and lactating women to achieve good fetal DHA stores (9) as during pregnancy, fetus depends completely on maternal sources of DHA. During infancy DHA needs of the baby are met through breast milk. During early childhood, DHA requirement are met by consumption of DHA rich food. However it has been found that DHA in average diet is very little due to westernization of diet as well poor intake of fish in diet, vegetarians who do not take even eggs or milk products, can only obtain DHA through the very limited conversion of dietary ALA. (10). In Canadian children between 4-7 year of age and not living near a marine environment, dietary intakes of DHA & AA are relatively low. Retinal and neuronal development continues throughout childhood, therefore it is conceivable that low intake a AA and DHA may have negative impact (11). Most Indians consume omega–6 and omega-3 fatty acids in ratio of 30-70:1 but ideal ratio is 5-10:1 for optimal health benefits (12).
Effects of DHA :
Brain : DHA is one of the major building structure of membrane phospholipids of brain. Epidemiological studies have linked low maternal DHA to increased risk of poor child neural development and intervention studies have shown decrease in risk of poor neural development (13). Neurodevelopment and cognitive abilities are enhanced by n-3 PUFA through breast milk or DHA-fortified food (14). Furthermore, there is increasing evidence that increased intake of DHA may confer benefits in a variety of psychiatric and neurological disorders and in particular neurodegenerative conditions. In addition, it may also have significant neuroprotective potential in acute neurological injury (15).
Vision : Light sensitivity of retinal rod photoreceptors is significantly reduced in newborns with DHA deficiency and DHA supplements significantly enhance visual acuity maturation (3).
Achieving Optimal Eye Function
Beyond development, the eyes and the brain need plentiful stores of DHA to function optimally. Cells in the retina, brain and other parts of the nervous system have connecting arms that transport electrical currents, sending visual information from the retina to the brain and messages from the brain throughout the body. DHA supplementation ensures the optimal composition of cell membranes necessary for the most effective transmission of these signals. DHA is correlated with improved visual and mental function.
In young infants and children
The development of both the retina and visual cortex are dependent on DHA. The retina develops rapidly during the final months of pregnancy and the first six months of infancy. Studies found that the eyesight of full term babies fed DHA enriched formula was measurably more acute than that of babies fed formula without DHA.
DHA affects the eye’s ability to distinguish fine spatial detail such as closely spaced lines, known as visual resolution acuity. Children’s vision continues to develop throughout their preschool years and eye/hand/body coordination, eye teaming, depth perception continues. Infants who do not obtain enough DHA during fetal development (pregnancy) have sub-optimal visual acuity and less DHA in their retinas. These differences are especially notable in infants born preterm. In term infants, differences in visual acuity are less consistent, in part because term infants have some DHA in their body fat.
In aging, visual function usually declines owing to changes in retina and other eye cells. Cell membranes lose some of their fluidity, cell structure changes, deposits accumulate, oxidation causes damage and cells are lost. These changes contribute to impaired vision in later life.
In age-related macular degeneration (AMD), yellowish deposits (drusen) accumulate in the macula, the central region of the retina .Cells in the macula break down and vision becomes distorted and blurry. Vision loss may develop. Drusen may develop into advanced forms of AMD, threatening the ability to see. As the most common or dry type of AMD progresses, the macular cells break down. Finally, the macular cells break down and central vision becomes severely impaired.
Second type of AMD, known as wet or neovascular AMD, is responsible for 90% of the vision loss in this condition. In wet AMD, the blood vessels behind the eye become abnormal and fragile, risking leakage and hemorrhage. Advanced AMD may affect one or both eyes and either wet or dry type can lead to blindness.
More recently, fish consumption twice a week or more was linked to significantly lower risk of AMD in a study of twins. Smoking increased the risk nearly 2-fold. Interestingly, in patients with advanced AMD, higher omega-3 PUFA consumption was associated with lower risk of the condition, but only when omega-6 or vegetable PUFA consumption was low. People with higher vegetable fat or linoleic acid (an omega-6 PUFA) intakes were more likely to develop AMD.
Studies suggest that the type of fat we consume can reduce or increase the chance of developing AMD. High intakes of polyunsaturated vegetable oils may increase the chance of developing the condition and undermine the effects of fish oil omega-3s. Boosting fish and fish oil consumption may lower the chance of developing AMD and slow its progress once it has started. Whether omega-3s can prevent the condition we do not know.
Hyperlipidemia in children : Recent research shows that DHA supplementation restores endothelial – dependant flow – mediated dilatation in hyperlipidemic children and has potential for preventing progression of early coronary heart disease in high risk children (16).
Other effects : Though DHA has been tried for behavioral alteration in children with autism its role still remains undefined (17). DHA had been found to inhibit growth of human colon carcinoma cells but its role in treatment of cancer remains undefined (18).
DHA is an omega 3 essential fatty acid indispensable for functions of brain and retina. In infants and children, better mental processing scores, psychomotor development and stereo acuity are associated with DHA intake (6). Diet being poor in DHA in pre-schoolers and non-breast led infants, DHA fortified food helps to maintain plasma phospholipids DHA content in children.
|Role of DHA on respiratory infections: |
|There have been recent reports of impact of DHA in decreasing incidence of respiratory infections in children upto 3 years of age (2,3). In study in USA, it was found that children who were given DHA with arachidonic acid (ARA) had significantly lower odds for developing upper respiratory infections (URI), wheezing/asthma or any allergy (2). In another study in Kansas city, USA it was found that children between 18-36 months who were given formula with DHA had higher RBC DHA and fewer adverse events and a lower incidence of respiratory illness (p = 0.024) compared to formula without DHA. Thus the authors concluded that modest increase in DHA intake in toddlers might improve respiratory health. (3). Saedisomeolia et al found that DHA reduces the release of inflammatory mediators from airway epithelial cells infected with rhinovirus (RV) (4) |
|Effect of DHA on inflammatory markers:|
|In vitro studies demonstrate DHA inhibits the expression of inflammatory markers such as pro-inflammatory cytokines, monocyte adhesion to endothelial cells (5). This may also have a protective effect on atopy and research from South Korea suggests that reduced content of n-3 PUFA in the RBC membrane could play a role in early children atopy (6). A number of studies have demonstrated that both Eicosapentaenoic acid (EPA) and DHA are bioactive and suppress antigen-specific delayed hypersensitivity reactions and mitogen-induced proliferation of T-cells, as well as modulate murine T-helper cell (Th1/Th2) balance (7). In general, the consumption of EPA and DHA are associated with lower levels of inflammatory mediators and soluble adhesion molecules.
Lopez-Alarcon et al supplemented neonates who developed sepsis after a surgical procedure with 100 mg of DHA for 14 days. They found that orogastric DHA administered in the acute phase of infection protects the nutritional status of neonates with sepsis. (8)
|DHA Supports Intelligence, Attention Span and Good Behaviour in Children|
|Docosahexaenoic acid (DHA) is sometimes referred to as “brain food” for good reason. Fats make up 60% of the brain and the nerves that run every system in the body, and DHA is the main structural component of brain tissue. Studies are showing that this long-chain omega-3 fatty acid has a huge impact on the developing brain, and may even determine how well children act, mentally and socially.
The omega-3 plays an important role in brain and central nervous system development and function, psycho-motor development (such as eye-hand coordination), visual development and function, and nerve signal transmission
Low DHA Levels Yield Disadvantages :
Studies have shown that pre-term infants, born without the benefit of the maternal delivery of DHA during the period of most rapid brain growth, the last trimester of pregnancy, did not perform as well on cognitive mental tests later in life. Specific behavioural and learning problems have also been shown to correlate significantly with low DHA levels.
DYSLEXIA - A learning disorder marked by impairment of the ability to recognize and comprehend written words, has been correlated with suboptimal DHA levels.
AUTISM - Autism is a neurodevelopmental disability with an increasing prevalence. Traditional medicine does not offer any cures for autism. Patients with autism spectrum disorders tend to have greater prevalence of gastrointestinal disorders. Many autism patients have food aversion and are picky eaters. Many parents have undertaken complementary and alternative treatments especially nutritional interventions. Omega-3 fatty acid (n-fatty acids) supplementation has been advocated by many experts. Omega-3 fatty acid supplements are part of 12-step autism treatment program.
ADHD - Children with Attention Deficit Hyperactivity Disorder or ADHD also have low DHA levels and experience essential fatty acid deficiency symptoms including hyperactivity and short attention span, frequent urination , frequent thirst. Studies have found that omega-3 fatty acids helped improve behavioural symptoms, Nutrient deficiencies are common in ADHD, and supplementation with minerals, the B vitamins, omega-3 and omega-6 fatty acids, and flavonoids have potential to decrease ADHD symptoms.
At this time, we do not know with certainty whether fatty acid abnormalities associated with ADHD are the result of differences in diet, genetic factors or fatty acid metabolism. So far, we know that children with ADHD who have low amounts of omega-3 EPA and DHA in their bodies have more learning and behavioural problems than those with normal amounts.
We do not know the optimal amount of omega-3s and omega-6s given separately or together that are most effective in different types of ADHD. However, preliminary evidence from treatment trials suggests that long-chain omega-3s may be a useful adjunctive treatment for ADHD and related childhood developmental conditions. Ensuring that the diet provides a regular source of long-chain omega-3s through eating fish twice a week as recommended by the American Heart Association, or consuming fish oil supplements or omega-3-enriched eggs is a reasonable approach for someone with ADHD.
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