DHA plays an important role in the evolution of the human brain, and archaeological investigations have found that DHA is the key to improving the brain-to-body mass ratio, representing improved cognitive ability, better concentration, planning and problem-solving skills, and more complex language, social, emotional and behavioral development. Note 13
What are the benefits of DHA in empirical medicine? Are there side effects or contraindications? See text analysis for details.
What is DHA?
DHA (Docosahexaenoic acid) and EPA (eicosapentaenoic acid) belong to omega‐3 long-chain polyunsaturated fatty acids (n-3 LCPUFA).
Of the two, DHA is the most important and abundant omega-3 long-chain polyunsaturated fatty acid in the brain (accounting for more than 90%, about 10%-20% of total lipids), and high levels of DHA have been identified in the gray matter of the brain and in the external rod segment of the retina.
In addition, DHA functions as a precursor to several metabolites and as a regulator of the central and enteric nervous systems and is involved in a variety of physiological processes, including membrane mobility, lipid raft function, neurotransmitter release, transmembrane receptor function, gene expression, signal transduction, myelination, neuroinflammation, neuronal differentiation and growth etc..
What are the recommended benefits of DHA?
1. Beneficial age-related cognitive decline
Cognition is a collective term that generally refers to mental processes that require the ability to remember and recall information, as well as the logical and abstract use of information to complete tasks that require sustained attention.
Changes in brain structure, neural activity, and biochemical characteristics are responsible for cognitive decline. In particular, increased oxidative stress, increased inflammation, and damage to blood vessels all play a role in age-related cognitive decline.
A systematic literature review and meta-analysis (10 randomized controlled trials, 2327 older adults) noted that DHA supplementation had no significant/beneficial effect in slowing/improving ageing decline in memory, executive function, working memory, and attention. Note 1
*Conclusion: For age-related cognitive decline, DHA supplementation did not bring significant benefits, but due to small sample sizes and heterogeneity between studies, more studies are needed to further validate
2. Beneficial bronchopulmonary dysplasia
Bronchopulmonary plasia (BPD) is the most common chronic lung disease in premature infants. Over the past few years, significant advances in perinatal care, including antenatal steroid therapy, surfactant use, and improvements in ventilator strategies, have improved survival rates for preterm infants.
However, the incidence of BPD has not decreased, with bronchopulmonary dysplasia occurring in approximately 40% of very low birth weight infants (birth weight < 1000 g) each year in the US, with potential risk factors including preterm birth, low birth weight, genetic predisposition, prolonged mechanical ventilation, hyperoxia, infection, and patent ductus arteriosus.
A systematic literature review and meta-analysis (5 randomized controlled trials with 1,966 preterm infants younger than 33 weeks’ gestational age) noted that DHA supplementation did not reduce the risk of bronchopulmonary dysplasia in preterm infants aged 32 weeks. Note 2
In addition, DHA supplementation did not significantly reduce the risk of other neonatal morbidities, including death, BPD at 28 days of birth, necrotising enterocolitis, ventricular haemorrhage, severe retinopathy of prematurity, or sepsis.
*Conclusion: DHA supplementation may not have a significant clinical effect in the treatment of bronchopulmonary dysplasia and other neonatal diseases
3. Beneficial attention deficit hyperactivity disorder
Attention-deficit hyperactivity disorder is one of the most common neurodevelopmental disorders that occurs in childhood but can persist into adulthood. The overall prevalence is 7.2%, with a higher prevalence in males than females, and is most common in school-age children.
Symptoms include inattention, hyperactivity/impulsivity, or both, leading to serious problems with social behavior and peer relationships, and are caused by genetic and environmental factors.
One randomized, double-blind, placebo-controlled trial (6 months, 66 patients aged 6 to 18 years with ADHD) noted greater improvements in cognitive domains with DHA supplementation. Note 3
*Conclusion: DHA supplementation may bring positive help for attention deficit hyperactivity disorder, but limited by small sample sizes, more studies are needed to further validate
4. Beneficial for fetal brain development (supplementation during pregnancy)
For fetuses and children to develop well, a variety of nutrients are required, and the DHA in omega-3 fatty acids is often of particular concern
Both animal and human studies have found that DHA is important for the development of the central nervous system and is key to determining cognition, behavior, and executive ability. Note 1
A randomized clinical trial (7-year follow-up period, 543 children) found that DHA supplementation in pregnant women in the second half of pregnancy did not significantly improve the intelligence quotient (IQ) language, learning, and executive skills of young children compared with placebo (only slightly better than perceptual reasoning). Note 2
In addition, the DHA group had more executive dysfunction (as measured by Global Executive composite) and behavioral problems (measured by the Strengths and Difficulties Questionnaire) than the control group
*Strengths and Difficulties Questionnaire (SDQ): Used primarily to assess emotional symptoms, behavioral problems, hyperactivity, inattention, peer relationships, and prosocial behavior
*Global Executive composite: Primarily used to assess behavioral regulation and metacognitive abilities
*Conclusion: Although DHA is theoretically helpful for brain development, the benefit of pregnancy supplementation on improving children’s intelligence is still unclear and needs to be confirmed by more studies in the future
5. Prevention and adjuvant treatment of cancer
Cancer is one of the most threatening of many diseases, comparable to cardiovascular disease, with an estimated 1 million people diagnosed with cancer worldwide each year, and nearly half of men and 4% of women in the United States develop cancer in their lifetime.
In a paper review, it was mentioned that DHA not only has the effect of inducing DNA oxidative damage in cancer cells, thereby promoting apoptosis of cancer cells, but also improves the sensitivity of tumor tissues to anticancer drugs and improves the therapeutic effect. Note 1
*Conclusion: DHA supplementation alone may have potential anti-cancer or anti-cancer effects, but most studies are limited to in vitro cell experiments, and human studies are still lacking
4. Prevent age-related macular degeneration
Age-related macular degeneration is one of the main causes of blindness in Western countries (the average incidence is about 8.01%), the early stage of the disease is mainly macular pigment abnormalities and choroidal drusen, when progressing to the advanced stage, depending on the disease will cause irreversible progressive vision loss. Note 6
A large prospective study (Prospective cohort study, up to 28 years, about 11,3 participants), consuming more omega-17 fatty acids (especially DHA) helped reduce the risk of early macular degeneration by 40% to 5% (but the effectiveness in preventing advanced macular degeneration is still unknown). Note 5
The mechanism behind it may be related to DHA’s anti-inflammatory and angiogenic inhibitory properties
*Conclusion: DHA intake from the diet can help prevent or even slow down the incidence of age-related macular degeneration, but more double-blind controlled studies are still needed to further confirm
5. Improve cognitive deterioration and prevent dementia
Cognitive decline is the main feature of aging, of which memory degeneration is the most distressing, second only to cardiovascular disease.
According to statistics, about 22.2% of the middle-aged and elderly population in the United States (more than 5 million people) have cognitive dysfunction, and 12% of them develop dementia within one year.
A follow-up study (9.1 years, in older adults without dementia, with an average age of 76 years), found that the people with the highest blood concentrations of DHA reduced the incidence of all-cause dementia by 47%. Note 7
Another double-blind controlled study (24 weeks, 485 healthy middle-aged and elderly people) found that DHA supplementation helped improve learning and memory function for age-related cognitive decline. Note 8
*Conclusion: DHA may be helpful for early cognitive impairment and reducing the incidence of dementia, but the effect of improving dementia is still unknown
The inflammatory response is a complex series of mechanisms by which the body repairs tissues and restores physiological balance in response to cellular damage caused by trauma or infection.
If the tissue is not completely repaired or the cause of inflammation is not ruled out, chronic inflammation will form at this time, which is an important factor in Alzheimer’s disease, atherosclerosis, diabetes and cancer. Note 10
A randomized, double-blind controlled study (10 weeks, 154 obese abdomen with low-order inflammatory response) showed that DHA had a superior anti-inflammatory effect (reduced interleukin-18 and 16, C-type reactive protein (CRP), tumor necrosis factor (TNF-α)) compared with EPA. Note 9
Are there side effects of DHA?
DHA products are very safe for most people to use in moderation, but side effects have been reported such as loose stools, stomach upset, hiccups, nausea, etc., and taking them with meals can reduce these conditions.
In addition, DHA products often contain EPA, EPA has the effect of reducing blood viscosity and thinning blood, excessive or long-term use may reduce coagulation function and increase the risk of bleeding.
Safety precautions (contraindicated for use)
DHA has a blood pressure or blood sugar lowering effect, and patients with high blood pressure, diabetes or taking related drugs should be aware that it may cause low blood pressure or hypoglycemia.
Do not use in people with coagulopathy, those taking anticoagulants and those who want to have surgery (in the first 3 weeks) (may increase the risk of bleeding).
Pregnant women, children and nursing mothers should consult a local doctor or pharmacist before using any supplements.
What are the foods rich in DHA?
Seafood and its by-products are known to contain high amounts of omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFAs), including DHA. However, marine animals themselves do not produce n-3 LCPUFA. They accumulate n-3 LCPUFA in the body by eating marine microalgae and other smaller marine animals that produce polyunsaturated fatty acids.
Traditionally, cold-water fish, mainly fatty fish, have been considered the main dietary source of DHA, such as salmon, mackerel, catfish, and trout. These fish can provide about 100.0 to 68.1 grams of DHA per 43 grams of meat. In addition, the meat of animals fed with seafood byproducts or microalgae rich in polyunsaturated fatty acids and the milk and eggs they produce also contain DHA.