Health Benefits of DHA - An Omega-3 Fatty Acid in Fish and Algae
What is DHA?
Docosahexaenoic acid, or DHA, is an omega-3 fatty acid found in oily fish. Like EPA (eicosapentaenoic acid), another omega-3 fatty acid found in fish, DHA has a range of valuable health benefits. Since nutritionists often refer to DHA and EPA at the same time, to the general public it may seem like the two substances have identical effects in our body. DHA offers special health benefits, however.
While oily fish are the best source of DHA, there are other sources which can be helpful for vegetarians and vegans. Vegetarians eat plants, dairy foods and eggs, but no fish or meat. Vegans eat no food that comes from animals.
Some vegetarian and vegan foods are enriched or fortified with DHA, EPA or both of these fatty acids. DHA is produced by certain types of algae and can be purchased in health food stores. The omega-3 fatty acid in plants is most commonly alpha-linolenic acid, or ALA. ALA can be converted to DHA and EPA in our bodies, although this conversion isn't very efficient.
DHA Health Benefits in Humans
When investigating DHA health benefits, it's important to distinguish hype from facts and to get information from independent and authoritative websites instead of (or as well as) from the websites of companies that sell DHA.
A report on health claims for DHA has been created by the European Food Safety Authority (EFSA). The report is based on the analysis of scientific research and reaches the following conclusions about DHA's benefits. Docosahexaenoic acid is said to:
- lower the level of blood triglycerides if taken in a sufficient daily dose
- help maintain normal brain function (a "well-established" benefit)
- help maintain the health of the retina and normal vision (also a well-established benefit)
The EFSA considers the following proposed benefits of DHA to be unproven.The chemical may or may not:
- reduce the level of oxidized cholesterol
- help to maintain normal weight
- help to maintain normal sperm mobility
Docosahexaenoic Acid Lowers Triglycerides
A triglyceride is a fat molecule. Although too many triglycerides are unhealthy, they are vital molecules. They are normally stored in fat cells and provide our body with energy when needed.
A high level of triglycerides in the blood is known as hypertriglyceridemia. The condition is dangerous because it increases the risk of heart disease and strokes. DHA has been shown to lower a high triglyceride level.
DHA Helps to Maintain Normal Brain and Eye Function
DHA is incorporated into the phospholipid molecules in cell membranes, especially those of our brain cells and retina cells. The retina is the light-sensitive layer at the back of the eyeball. DHA is thought to help the membranes function properly.
DHA is beneficial for brain function and cognition as well as sight. It seems to be very important in the outer membranes of neurons (nerve cells), especially in those involved in the transmission of nerve impulses from one neuron to another.
DHA and Memory
There are other suspected health benefits of DHA. A link between DHA in the diet and improved memory has often been observed.
A team of researchers at the University of Alberta discovered that lab animals fed a diet high in docosahexaenoic acid stored more of the chemical in the hippocampus area of their brain, which plays an important role in memory. They also found that the cells in the hippocampus could communicate with each other better when more DHA was present. These processes might explain why the chemical seems to improve memory. The amount of DHA in the brain decreases with age, so ensuring that the diet contains this nutrient may help maintain memory as we grow older.
A low brain level of docosahexaenoic acid seems to be a risk factor for Alzheimer's disease. As yet, it's unknown if the nutrient can treat the disease.
Omega-3 Fatty Acids and Learning
DHA and Suicide Risk in the Military
A group of scientists investigated the level of omega-3 fatty acids in the brains of 800 military service members who had committed suicide and in 800 service members matched with the people who had committed suicide with respect to gender, age and rank.
The scientists found that all of the people tested had a low level of omega-3 fatty acids in their body. They also found that the suicide risk was greatest in people who had the lowest level of DHA. Previous research has also suggested that the level of docosahexaenoic acid in the body may be significant in some mental health problems.
DHA and Liver Disease
As obesity increases in North America, so does the incidence of liver disease. According to the American Liver Foundation, about 25% of the U.S. population have nonalcoholic fatty liver disease. This includes about 75% of the obese population. Fatty liver disease may progress to more serious disorders, including cirrhosis of the liver, liver cancer and a condition known as nonalcoholic steatohepatitis, or NASH, all of which may be fatal.
When a person develops NASH, the liver becomes scarred during a process called fibrosis. In studies involving lab animals, researchers found that DHA reduced the level of proteins found in NASH fibrosis by more than 65%. EPA had "comparatively little" effect on the protein level.
DHA and Fetal Development
DHA passes through the placenta from a woman to her fetus and is essential for the development of her baby's brain and vision. DHA supplements are often recommended for pregnant women for this reason. However, some research suggests that the fetus gets all the DHA that it needs from its mother's body - even without supplementation - and that supplementation isn't beneficial. Older research suggested that DHA supplementation is helpful for a developing baby, although some of the research didn't differentiate between DHA and EPA. This is an area that needs much more investigation.
Once the baby is born, he or she continues to receive DHA through the mother's milk. Docosahexaenoic acid is added to many infant formulas for those babies who don't drink milk made by their mother.
DHA in Pregnancy and Lactation
Pregnant and lactating women should seek their doctor's advice about DNA supplementation and about the use of any other supplements.
Sources of DHA
The best way to get DHA is in the diet. Oily fish such as wild salmon, some tuna, sardines, herring and mackerel are very good sources of both EPA and DHA. So are krill. Krill are small crustaceans that live in oceans around the world.
There are potential problems with getting omega-3 fatty acids from fish or krill. In order for the animals to be a wise food choice, they need to be low in mercury. Mercury is an ocean pollutant and is toxic. In addition, the fishing industry used to harvest the animals needs to be sustainable.
Enriched and Fortified Food
Some eggs contain a higher than normal level of omega-3 fatty acids. DHA and/or EPA are added to some varieties of milk, orange juice and breakfast cereals. A consumer should investigate the type and source of omega-3 fatty acids in enriched and fortified foods. For example, some chickens that produce enriched eggs are fed fish oil. This may be considered unacceptable by vegetarians and vegans.
Certain microscopic marine algae, or microalgae, produce DHA. The algal cells are cultured in a special facility and then processed to extract their oil. The oil is rich in DHA and is free of ocean pollution. It's popular with some vegans since it's obtained without killing animals.
Some people obtain omega-3 fatty acids by taking fish oil supplements instead of algal oil supplements. It's important that the correct dose of a supplement is taken. Too much could be dangerous, while too little could have no effect on the body. The purity and freshness of the oil also need to be considered.
An Omega-3 Poll
Do you take an omega-3 supplement?See results without voting
Docosahexaenoic Acid in the Future
Tantalizing observations suggest that docosahexaenoic acid may have wonderful health benefits, but the results of some experiments with the chemical have been disappointing. More research is needed to clarify the functions of DHA in our bodies. For example:
- How do DHA's effects differ from EPA's effects?
- Does DHA have different effects at different times in our lives or in different stages of fetal development?
- Does it need other nutrients in order to function best?
- What dose is helpful and what dose is harmful?
- Is DHA more beneficial in food than in supplements, or vice versa?
Despite some uncertainty about the actions of DHA, the evidence obtained so far indicates that it's a valuable nutrient. Ensuring that our diet contains DHA is definitely worthwhile.
References and Further Reading
© 2013 Linda Crampton
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