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What are DHA, EPA, and LNA?
DHA is the abbreviation for docosapentaenoic acid; EPA (in this context) is the abbreviation for eicosapentaenoic acid; and LNA stands for alpha-linolenic acid. All of these acids are polyunsaturated fatty acids that you can obtain through foods. DHA and EPA are abundant in the flesh and oils from cold water fish such as mackerel and cod. LNA is found in certain plant oils; it is most abundant in flaxseed oil, canola oil, and soybean oil, and can also be found in tofu and nuts.
Can DHA and EPA be substituted by taking LNA?
In the body, LNA can be converted to EPA and DHA. However it appears that you need relatively large amounts of LNA to form enough EPA and DHA to meet the recommendations for these fatty acids. Exactly how much more has not been determined, because the rate of conversion of LNA to EPA and DHA in humans is not known. It is very likely that the rate of conversion varies by age, gender, and type of tissue in the body (for example, the rate in the brain may be higher than the rate in the liver). Therefore, taking large amounts of LNA may not be an effective alternative to consuming DHA and EPA.
For vegetarians, is it acceptable that DHA and EPA can only come from fish oil supplements?
As you can see, DHA and EPA work at many levels to decrease cardiovascular disease. Some of these processes are also changed by adopting a vegetarian diet, whether you eat fish oils or not. For example, people on vegetarian diets seem to develop less plaque in their arteries than do people on omnivore diets that do not contain fish oils. The exact mechanism for these differences is not known, but part of the difference may be due to the lower cholesterol levels seen in people on vegetarian diets.
Nevertheless there is one dissenting study, which you can find discussed in the American Heart Association's webpage, entitled "Fish diet better than vegetarian fare at lowering lipoprotein (a) -- one `bad' fat", in which fish may provide protection above what can be provided by a vegetarian diet.
So it would seem that vegetarians who will not eat fish oils can probably get at least some of their benefit from other sources. The benefit may come in part through the vegetarian diet itself, and in part through the consumption of certain vegetable oils, although the amount of vegetable oils a person should consume is not known.
Are fish oil supplements safe? I have read that these supplements may be contaminated with PCBs.
As you probably know, fish which swim in PCB contaminated waters, such as the waters found in the Great Lakes, and in many other bodies of fresh and salt water around the world, can accumulate PCBs in their flesh and oils. PCBs, or polychlorinated biphenyls, are fat soluble and are not degraded, so they can accumulate in fat tissue if you eat fish contaminated with these chemicals. The amount of these contaminants in fish oils varies considerably. Part of the variation comes from the source of the fish, in other words the extent to which the fish is contaminated, and part comes from the way the fish oils are prepared.
PCBs themselves, or other fish contaminants for which the presence of PCBs may be a marker, are particularly harmful for fetuses, infants, and children, where they can cause varying degrees of growth failure, mental retardation, and increased death just before and after birth (that is, increased perinatal mortality). Women of reproductive age should avoid sources of PCBs as best they can.
In other adults, the relationship of PCBs to health problems is less clear, because most of the studies linking health consequences to PCBs have been done in animals. In animals, PCBs are carcinogenic; they decrease some measures of immune responsiveness; and they alter thyroid and sex hormone metabolism.
While changes in thyroid status have been reported to be associated with PCBs in humans, and there is reason to believe that certain PCBs affect the metabolism of sex hormones and steroids, obvious consequences of these hormonal changes have not been clearly demonstrated in humans.
There has been some question whether PCBs may contribute to the development of cancer, because workers exposed to PCBs do develop liver cancer and malignant melanoma more often than wokers not exposed to PCBs on their jobs. However, there has been no evidence to date that people exposed to PCBs through foods have a higher incidence of cancer than people not so exposed. One particular concern has been the development of breast cancer. In at least one study which appeared this year (Serum concentrations of organochlorine compounds and the subsequent development of breast cancer, by Kathy J Helzlsouer and her colleagues, published in Cancer Epidemiology Biomarkers and Prevention, June, 1999, Volume 8, pages 525-532), the higher levels of PCBs were associated with a lower incidence of breast cancer!
Therefore, more studies are needed to determine what effects PCBs may have on adult health.
Consuming vegetable oil instead of fish oil may decrease your exposure to PCB contamination. However, keep in mind that plants contain compounds which can affect adult hormonal status -- and in particular thyroid and sex hormone status -- directly or indirectly, in what appears to be much the same way as PCBs.
DHA is the abbreviation for docosapentaenoic acid; EPA (in this context) is the abbreviation for eicosapentaenoic acid; and LNA stands for alpha-linolenic acid. All of these acids are polyunsaturated fatty acids that you can obtain through foods. DHA and EPA are abundant in the flesh and oils from cold water fish such as mackerel and cod. LNA is found in certain plant oils; it is most abundant in flaxseed oil, canola oil, and soybean oil, and can also be found in tofu and nuts.
Can DHA and EPA be substituted by taking LNA?
In the body, LNA can be converted to EPA and DHA. However it appears that you need relatively large amounts of LNA to form enough EPA and DHA to meet the recommendations for these fatty acids. Exactly how much more has not been determined, because the rate of conversion of LNA to EPA and DHA in humans is not known. It is very likely that the rate of conversion varies by age, gender, and type of tissue in the body (for example, the rate in the brain may be higher than the rate in the liver). Therefore, taking large amounts of LNA may not be an effective alternative to consuming DHA and EPA.
For vegetarians, is it acceptable that DHA and EPA can only come from fish oil supplements?
As you can see, DHA and EPA work at many levels to decrease cardiovascular disease. Some of these processes are also changed by adopting a vegetarian diet, whether you eat fish oils or not. For example, people on vegetarian diets seem to develop less plaque in their arteries than do people on omnivore diets that do not contain fish oils. The exact mechanism for these differences is not known, but part of the difference may be due to the lower cholesterol levels seen in people on vegetarian diets.
Nevertheless there is one dissenting study, which you can find discussed in the American Heart Association's webpage, entitled "Fish diet better than vegetarian fare at lowering lipoprotein (a) -- one `bad' fat", in which fish may provide protection above what can be provided by a vegetarian diet.
So it would seem that vegetarians who will not eat fish oils can probably get at least some of their benefit from other sources. The benefit may come in part through the vegetarian diet itself, and in part through the consumption of certain vegetable oils, although the amount of vegetable oils a person should consume is not known.
Are fish oil supplements safe? I have read that these supplements may be contaminated with PCBs.
As you probably know, fish which swim in PCB contaminated waters, such as the waters found in the Great Lakes, and in many other bodies of fresh and salt water around the world, can accumulate PCBs in their flesh and oils. PCBs, or polychlorinated biphenyls, are fat soluble and are not degraded, so they can accumulate in fat tissue if you eat fish contaminated with these chemicals. The amount of these contaminants in fish oils varies considerably. Part of the variation comes from the source of the fish, in other words the extent to which the fish is contaminated, and part comes from the way the fish oils are prepared.
PCBs themselves, or other fish contaminants for which the presence of PCBs may be a marker, are particularly harmful for fetuses, infants, and children, where they can cause varying degrees of growth failure, mental retardation, and increased death just before and after birth (that is, increased perinatal mortality). Women of reproductive age should avoid sources of PCBs as best they can.
In other adults, the relationship of PCBs to health problems is less clear, because most of the studies linking health consequences to PCBs have been done in animals. In animals, PCBs are carcinogenic; they decrease some measures of immune responsiveness; and they alter thyroid and sex hormone metabolism.
While changes in thyroid status have been reported to be associated with PCBs in humans, and there is reason to believe that certain PCBs affect the metabolism of sex hormones and steroids, obvious consequences of these hormonal changes have not been clearly demonstrated in humans.
There has been some question whether PCBs may contribute to the development of cancer, because workers exposed to PCBs do develop liver cancer and malignant melanoma more often than wokers not exposed to PCBs on their jobs. However, there has been no evidence to date that people exposed to PCBs through foods have a higher incidence of cancer than people not so exposed. One particular concern has been the development of breast cancer. In at least one study which appeared this year (Serum concentrations of organochlorine compounds and the subsequent development of breast cancer, by Kathy J Helzlsouer and her colleagues, published in Cancer Epidemiology Biomarkers and Prevention, June, 1999, Volume 8, pages 525-532), the higher levels of PCBs were associated with a lower incidence of breast cancer!
Therefore, more studies are needed to determine what effects PCBs may have on adult health.
Consuming vegetable oil instead of fish oil may decrease your exposure to PCB contamination. However, keep in mind that plants contain compounds which can affect adult hormonal status -- and in particular thyroid and sex hormone status -- directly or indirectly, in what appears to be much the same way as PCBs.
