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Most healthy people do not supplement with fish oil containing DHA or vegetarian sources of DHA. The level of DHA given to premature infants who are not breast-fed should be determined by a pediatrician. Much of the research in adults has been based on 1–3 grams per day of DHA from fish oil, although higher levels have been taken when isolated DHA from microalgae sources is used.
Because cod liver oil contains large amounts of vitamin A and vitamin D, women who are or who could become pregnant should consult a doctor before taking cod liver oil. Adults should make sure the total amount of vitamin A and vitamin D from cod liver oil and other supplements does not exceed 25,000 IU (7,500 mcg) per day for vitamin A (15,000 IU per day for those over age 65) and 800 IU per day for vitamin D, unless they are being supervised by a doctor.
Cold-water fish, such as mackerel, salmon, herring, sardines, black cod, anchovies, and albacore tuna, are rich sources of DHA and EPA. Similarly, cod liver oil contains large amounts of DHA and EPA. Certain microalgae contain DHA and are used as a vegetarian source of this nutrient in some supplements. Most fish oil supplements contain 12% DHA.
Premature infants who are not breast-fed are often DHA-deficient.9 A link has appeared between DHA deficiency and Alzheimer’s disease; however, no evidence at this time indicates that supplementation with DHA will help Alzheimer’s patients.10 Similarly, preliminary evidence shows that children with attention deficit disorder (ADD) have low DHA levels. However, no evidence demonstrates that DHA supplementation improves ADD.11 Preliminary evidence suggests that people with a variety of rare but related congenital diseases (Zellweger’s syndrome, neonatal adrenoleukodystrophy, and infantile Refsum’s disease) may be DHA-deficient, and may even benefit from DHA supplementation.12 Many doctors believe the diets of most people eating a Western diet do not provide optimal amounts of omega-3 fatty acids.
At least four studies have reported a reduced blood level of omega-3 fatty acids in people with depression.13, 14, 15, 16
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The information presented by Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires December 2017.