Cod liver oil is a good source of long chain omega-3 fatty acids including eicosapentaenoic acid (EPA; one capsule generally provides 45 mg EPA) and docosahexaenoic acid (DHA; one capsule generally provides 22 mg DHA). Approximately 7% of cod liver oil is EPA and about 7% DHA by weight.
Cod liver oil is a rich source of vitamin A. In fact, one teaspoon of cod liver oil has 4,500 IU of vitamin A; one capsule generally provides 1,250 IU of vitamin A.
Cod liver oil is a source of vitamin D. One capsule contains approximately 130 IU of vitamin D.
The most conclusive research with cod liver oil indicates that this supplement reduces the pain and inflammation associated with arthritis. Research into cancer, depression, and cardiovascular disease is less convincing.
The recommended dosage of cod liver oil is 0.5 to 1.5 g of oil daily. This corresponds to one to three small capsules or less than 1/3 teaspoon. Care should be taken with liquid cod liver oil supplements as it is easy to take too much.
A safe upper limit would be 2/3 teaspoon or three small capsules (1.5 g of oil).
Specific toxicity from cod liver oil is not known. However, the very high concentration of vitamin A in cod liver oil contributes to potential toxicity from this supplement.
Symptoms of vitamin A toxicity include loss of appetite, headache, blurred vision, irritability, hair loss, drying and flaking of the skin, swelling in the extremities, drowsiness, diarrhea, nausea, and enlargement of the spleen and liver.
Recent reports indicate that too much vitamin A (retinol) daily can interfere with bone growth and promote fractures. Thus, care should be taken not to exceed the RDA for vitamin A, particularly if taking cod liver oil supplements with other vitamin A supplements (including multivitamins).
The elderly are at an increased risk for toxicity and should take extra care not to exceed the RDA for vitamin A if consuming cod liver oil supplements.
Vitamin A excess during the first trimester of pregnancy can result in severe craniofacial and oral clefts and limb defects of the fetus. High doses of vitamin A (retinol and retinyl esters) during pregnancy have been associated with birth defects. It is recommended that women who are pregnant or may become pregnant do not exceed the tolerable Upper Limits.1
Interactions due to vitamin A content of cod liver oil are the most likely:
Warfarin (Coumadin) is an anticoagulant. The risk of abnormal bleeding is increased when warfarin is taken with high-dose supplements of fat-soluble vitamins such as vitamin A. Vitamin A and warfarin should not be combined unless supervised by a physician or pharmacist. 2
Retinoid drugs, such as tretinoin (Retin-A), isotretinoin (Accutane), and 13-cis as well as all-trans-retinoic acids, are structurally similar to vitamin A. They are used topically and systemically for the reduction of acne and the appearance of wrinkles. People using these compounds should avoid vitamin A-containing supplements such as cod liver oil to avoid possible toxicity.
Information on the relationship between substances and disease is provided for general information, in order to convey a balanced review of the scientific literature. In many cases the relationship between a substance and a disease is tentative and additional research is needed to confirm such a relationship.
Cod liver oil (n-3 fatty acids) as an non-steroidal anti-inflammatory drug sparing agent in rheumatoid arthritis.
A double-blind, placebo-controlled clinical trial at two centers investigated the efficacy of cod liver oil for reduction of use of non-steroidal anti-inflammatory drugs (NSAIDs) in rheumatoid arthritis (RA). Ninety-seven people with RA enrolled in the nine-month trial; 58 completed the study (60%). Participants were randomly assigned to receive 10 g of cod liver oil containing 2.2 g of n-3 EFAs or air-filled identical placebo capsules daily for the duration of the trial. After 12 weeks of supplementation, participants were instructed to gradually reduce, and if possible, stop their NSAID intake; successful reduction of NSAID use was defined as more than 30% reduced use of NSAIDs. Thirty-nine percent (19/49) of participants in the cod liver oil group were able to reduce their NSAID use by at least 30%; ten percent of the placebo group (5/48) were able to reduce NSAID use by at least 30% (P=0.002, chi-squared test). Clinical parameters and severity of disease were not altered in either group during the study. The results of this study suggest that cod liver oil may help to limit the amount of NSAID drugs needed by people with RA. Further studies are needed to confirm this result. 3
Effect of cod liver oil on symptoms of rheumatoid arthritis.
A small pilot study investigated the efficacy of cod liver oil supplements on symptoms of rheumatoid arthritis. Forty-three people with rheumatoid arthritis participated in the study. Participants consumed 1 g cod liver oil daily for three months. Supplementation significantly reduced morning joint stiffness for 52.4% of participants (P<0.001). Joint pain was reduced in 42.7% of participants (P=0.001) and joint swelling was reduced in 40% of participants (P=0.001). Intensity of pain was reduced in 67.5% of participants. Sixty-eight percent of participants rated efficacy of cod liver oil as good or very good. Ninety-five percent of participants rated tolerability of cod liver oil as good or very good. The results of this pilot study suggest that cod liver oil significantly improves symptoms or rheumatoid arthritis. 4
Vitamin D and reduced risk of breast cancer: a population-based case-control study.
A population-based case-control study investigated the relationship between vitamin D and breast cancer. Women with newly diagnosed invasive breast cancer (972 cases) and women without breast cancer (1,135 controls) participated in the study. Increasing sun exposure between ages 10 and 19 was associated with reduced breast cancer risk (OR 0.65 for highest quintile vs. lowest, p=0.0006). Use of cod liver oil (OR 0.76; 95% CI, 0.62-0.92; P=0.0004) and consumption of milk (OR 0.62; 95% CI 0.45-0.86 for 10 or more glasses per week versus none; P=0.0004) were also associated with reduced breast cancer risk. These associations were weaker for ages 20 to 29 and no association was found for ages 45 to 54. These results suggest that sun exposure or vitamin D supplements reduce risk of breast cancer when exposure is early in life. The results of this epidemiologic study need to be confirmed.5
Associations between cod liver oil use and symptoms of depression: The Hordaland Health Study.
Data from the Hordaland Health Study were used to assess the association between cod liver oil use and depression or anxiety. The Hordaland Health Study included 21,835 men and women aged 40 to 49 years or 70 to 74 years and used the Hospital Anxiety and Depression Scale to assess depression and anxiety. Overall, 8.9% of the subjects used cod liver oil supplements daily. In the whole study population, 3.6% had depressive symptoms. When stratified for use of cod liver oil, however, only 2.5% of those using cod liver oil versus 3.8% of the remaining subjects had depressive symptoms (OR 0.71, 95% CI 0.52 to 0.97). The prevalence of depressive symptoms showed an inverse relationship with duration of use of cod liver oil supplements (0-12 months; P=0.04); only the subjects in the 40 to 46 year age group were studied in this assessment. These data suggest that the use of cod liver oil supplements may reduce incidence of depression.6
Serum retinoids and beta-carotene as predictors of hip and other fractures in elderly women.
A nested case-control study of older women (aged 75 years or more) investigated the relationships between vitamin A status and bone health. Three-hundred-twelve women with bone fractures (cases) and 934 women without fractures (controls) participated in the study. Serum retinol, retinyl palmitate, and beta-carotene were not significant independent predictors of hip fracture or any fracture. The hazard ratio (HR) for all osteoporotic fractures was HR 0.92 (95% CI 0.81-1.05, p<0.05) per 1 standard deviation increase in plasma retinol. In fact, risk of any osteoporotic fracture was slightly less in the highest versus the lowest quartile of plasma retinol (HR 0.85, 95% CI 0.69-1.05, p=0.132). Multivitamin or cod liver oil supplementation was associated with a significant reduction of risk for all fractures (HR 0.76, 95% CI 0.60-0.96, p=0.021). Thus, this study indicated no harmful association between plasma retinol status and bone health. These results indicate that multivitamins or cod liver oil supplements may be beneficial for bone health. Further clinical trials are needed to confirm these results before a supplementation recommendation is made.7
Divergent anti-inflammatory effects of different oil acute consumption on healthy individuals.
A randomized, parallel design trial investigated the effects of various oils on markers of inflammation in healthy adults. Sixty-seven healthy people participated in the trial. Participants were randomly assigned to receive 50 mL of extra virgin olive oil, soy oil, corn oil, or cod liver oil. Markers of inflammation were assessed by enzyme linked immunosorbent assay at baseline and three hours after consuming the oil. Vascular cell adhesion molecule 1 (VCAM-1) was not significantly altered by any of the oils (P=nonsignificant (NS) for all). Inter-cellular adhesion molecule 1 (ICAM-1) was decreased by all oils: olive oil (P<0.01), soy oil (P<0.01), cod liver oil (P<0.01), and corn oil (P<0.01). Tumor necrosis factor-á (TNF-á) levels were significantly reduced by olive oil (P<0.05), soy oil (P<0.01), and cod liver oil (P<0.01); corn oil nonsignificantly reduced levels of TNF-á. A significant correlation between the absolute change in ICAM-1 and TNF-á levels (p=0.379, P<0.05) was noted. There was no correlation between the absolute changes in VCAM-1 and TNF-á levels (p=0.019, P=NS). This preliminary study indicates that these different oils alter markers of inflammation in different ways. Further studies will help to evaluate the mechanisms and meanings of these effects.8
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