DHA (Docosahexaenoic Acid): A Detailed Review

Cod Liver Oil Capsules in a LidDocosahexaenoic acid (DHA) is one of the most important omega-3 fatty acids.

Like most omega-3 fats, it’s linked with many health benefits.

It is a part of every cell in your body, plays a vital role in your brain and is absolutely crucial during pregnancy and infancy.

Since your body can’t produce it in adequate amounts, you need to get it from your diet.

This article explains everything you need to know about DHA.

What is DHA (Docosahexaenoic Acid)?

Docosahexaenoic acid (DHA) is a long-chain omega-3 fatty acid.

It’s 22 carbons long, has 6 double bonds and is mainly found in seafood, such as fish, shellfish, fish oils and some types of algae.

It’s a component of every cell in your body and a vital structural component of your skin, eyes and brain (1, 2, 3, 4).

In fact, DHA makes up over 90% of the omega-3 fatty acids in your brain and up to 25% of its total fat content (3, 5).

Technically, it can be synthesized from another plant-based omega-3 fatty acid called alpha-linolenic acid (ALA). However, this process is very inefficient, and only 0.1–0.5% of ALA is converted into DHA in your body (6, 7, 8, 9, 10).

What’s more, the conversion also relies on adequate levels of other vitamins and minerals, as well as the amount of omega-6 fatty acids in your diet (11, 12, 13).

Because your body can’t make DHA in significant amounts, you need to get it from your diet or supplements.

Bottom Line: DHA is an omega-3 fatty acid that is vital for your skin, eyes and brain. Your body can’t produce it in adequate amounts, so you need to get it from your diet.

How Does it Work?

Doctor Holding a Glass of Water and Omega Capsules

DHA is an unsaturated fatty acid with 6 double bonds. This means it’s very flexible.

It’s mainly located in cell membranes, where it makes the membranes and gaps between cells more fluid (14).

This makes it easier for nerve cells to send and receive electrical signals, which is their way of communicating (15).

Therefore, adequate levels of DHA seem to make it easier, quicker and more efficient for nerve cells to communicate.

Having low levels in your brain or eyes may slow the signaling between cells, resulting in poor eyesight or altered brain function.

DHA also has various other functions in the body. For example, it fights inflammation and lowers blood triglycerides.

Bottom Line: DHA makes the membranes and gaps between nerve cells more fluid, making it easier for cells to communicate.

Top Food Sources of DHA

Herring

DHA is mainly found in seafood, such as fish, shellfish and algae.

Several types of fish and fish products are excellent sources, providing up to several grams per serving (16).

These include:

  • Mackerel.
  • Salmon.
  • Herring.
  • Sardines.
  • Caviar.

Some fish oils, such as cod liver oil, can provide as much as 1 gram of DHA in one tablespoon (10–15 ml) (17).

Just keep in mind that some fish oils may also be high in vitamin A, which can be harmful in large amounts.

DHA may also be present in small amounts in meat and dairy from grass-fed animals, as well as omega-3 enriched or pastured eggs.

However, it may be hard to get enough from your diet alone. So if you don’t regularly eat the foods mentioned above, taking a supplement may be a good idea.

Bottom Line: DHA is mostly found in fatty fish, shellfish, fish oils and algae. Grass-fed meat, dairy and omega-3 enriched eggs may also contain small amounts.

Effects on the Brain

Human Brain on White Background

DHA is the most abundant omega-3 in your brain and plays a critical role in its development and function.

Brain levels of other omega-3 fatty acids, such as EPA, are typically 250–300 times lower (3, 4, 18).

It Plays a Major Role in Brain Development

DHA is extremely important for brain tissue growth and function, especially during development and infancy (19, 20).

It needs to accumulate in the central nervous system in order for the eyes and brain to develop normally (3, 4).

DHA intake during the third trimester of pregnancy determines the baby’s levels, with the greatest accumulation occurring in the brain during the first few months of life (3).

DHA is mainly found in the gray matter of the brain, and the frontal lobes are particularly dependent on it during development (21, 22).

These parts of the brain are responsible for processing information, memories and emotions. They are also important for sustained attention, planning and problem solving, as well as social, emotional and behavioral development (4, 5, 23).

In animals, decreased DHA in a developing brain leads to a reduced amount of new nerve cells and altered nerve function. It also impairs learning and eyesight (24).

In humans, DHA deficiency in early life has been associated with learning disabilities, ADHD, aggressive hostility and several other disorders (25, 26).

Furthermore, studies have linked low levels in the mother to an increased risk of poor visual and neural development in the child (3, 24, 27).

Studies have shown that babies of mothers who consumed 200 mg per day from the 24th week of pregnancy until delivery had improvements in vision and problem solving (3, 28).

Bottom Line: DHA is essential for brain and eye development. A deficiency in early life is linked to learning disabilities, ADHD and other disorders.

It May Have Benefits for the Aging Brain

DHA is also critical for healthy brain aging (29, 30, 31, 32).

There are many factors that come naturally with brain aging, such as oxidative stress, altered energy metabolism and DNA damage (33, 34, 35).

The structure of the brain also changes, which reduces its size, weight and fat content (36, 37).

Interestingly, many of these changes are also seen when DHA levels decrease.

This includes altered membrane properties, decreased performance in memory tasks, altered enzyme activity and altered neuron function (38, 39, 40, 41, 42).

Taking a supplement may help. DHA supplements have been linked to significant improvements in memory, learning and verbal fluency for those with mild memory complaints (43, 44, 45, 46, 47, 48).

Bottom Line: A DHA deficiency may disrupt brain function. Supplements may improve memory, learning and verbal fluency for certain people.

Low Levels Are Linked to Brain Diseases

Elderly Man Thinking

Alzheimer’s disease is the most common form of dementia in older people.

It affects about 4.4% of adults over 65 and impacts brain function, mood and behavior (49, 50).

Changes in episodic memory are among the earliest signs of brain changes in older adults. This refers to difficulty recalling events that occurred at a specific time and place (44, 51, 52, 53).

Interestingly, Alzheimer’s disease patients have lower amounts of DHA in the brain and liver, while EPA and DPA levels are elevated (54, 55).

Studies show that higher blood DHA levels are linked to a reduced risk of developing dementia and Alzheimer’s (56).

Bottom Line: Low DHA levels are linked to an increased risk of developing memory complaints, dementia and Alzheimer’s disease.

Effects on Eyes and Vision

DHA is a very important membrane component in the eye. It helps activate a protein called rhodopsin, a membrane protein in the rods of the eye.

Rhodopsin helps your brain receive images from your eyes by changing membrane permeability, fluidity, thickness and other properties inside the eye (57, 58).

A DHA deficiency can cause vision problems, especially in children (3, 24, 27).

Therefore, baby formulas are now generally fortified with it, which helps to prevent vision impairment in babies (59, 60).

Bottom Line: DHA is important for vision and various functions inside the eye. A deficiency may cause vision problems in children.

Effects on Heart Health

Omega-3 fatty acids have generally been linked to a reduced risk of heart disease.

Low levels are associated with an increased risk of heart disease and death, and some (but not all) supplement studies have shown that omega-3s reduce the risk (61, 62, 63, 64).

This applies especially to the long-chain omega-3 fatty acids found in fatty fish and fish oils, such as EPA and DHA.

Their intake can improve many risk factors for heart disease, including:

  • Blood triglycerides: Long-chain omega-3 fatty acids may reduce blood triglycerides by up to 30% (65, 66, 67, 68, 69).
  • Blood pressure: The omega-3 fatty acids in fish oils and fatty fish may reduce blood pressure in people with high blood pressure (70, 71, 72).
  • Cholesterol levels: Fish oils and omega-3s may lower total cholesterol and increase HDL cholesterol in people with high cholesterol levels (73, 74, 75).
  • Endothelial function: DHA may protect against endothelial dysfunction, which is a leading driver of heart disease (76, 77, 78, 79).

Bottom Line: DHA may reduce the risk of heart disease by lowering blood triglycerides and blood pressure, improving cholesterol levels and protecting against endothelial dysfunction.

Other Health Benefits

DHA may also protect against the development of other diseases, including:

  • Arthritis: It reduces inflammation in the body and may alleviate the pain and inflammation in the joints of people with arthritis (80, 81).
  • Cancer: It may make it more difficult for cancer cells to survive. It may also cause them to die via programmed cell death (80, 82, 83, 84, 85).
  • Asthma: It may reduce asthma symptoms, possibly by blocking mucus secretion and reducing blood pressure (86, 87, 88).

Bottom Line: DHA may also help with conditions like arthritis and asthma, as well as prevent the growth of cancer cells.

DHA is Especially Important During Pregnancy, Lactation and Childhood

Fetus in Womb Icon

DHA is critical during the last months of pregnancy and early in a baby’s life.

Babies up to the age of two have a greater need for it than older children and adults (3, 89, 90).

Their brains are growing rapidly, and need high amounts of DHA to form vital cell membrane structures in the brain and eyes (3, 91).

Therefore, DHA intake can dramatically affect brain development (27, 92).

Animal studies show that DHA-deficient diets during pregnancy, lactation and weaning limit the supply to the infant’s brain to only about 20% of normal levels (93).

Deficiency is associated with changes in brain function, including learning disabilities, changes in gene expression and impaired vision (24).

Bottom Line: During pregnancy and early life, DHA is vital for the formation of structures in the brain and eyes.

How Much DHA Do You Need?

Fish Oil Capsules on a Wooden Spoon

Most guidelines for healthy adults recommend at least 250–500 mg of combined EPA and DHA per day (94, 95, 96, 97, 98, 99).

Studies show the average DHA intake is closer to 100 mg per day (100, 101, 102).

Children up to the age of two may need 4.5–5.5 mg/lb (10–12 mg/kg) of body weight, while older children may need up to 250 mg per day (103).

Pregnant or breastfeeding mothers are advised to get at least 200 mg of DHA, or 300–900 mg of combined EPA and DHA, per day (92, 96).

People with mild memory complaints or cognitive impairments may benefit from 500–1,700 mg of DHA per day to improve brain function (43, 44, 45, 46, 47, 48).

Vegetarians and vegans are often lacking in DHA and should consider taking microalgae supplements that contain DHA (11, 104).

DHA supplements are usually safe. However, taking more than 2 grams a day does not have any added benefits and is not recommended (105, 106).

Interestingly, curcumin — the active compound in turmeric — may enhance DHA absorption in the body. It’s linked with many health benefits, and animal studies have shown that it may boost DHA levels in the brain (107, 108).

Therefore, curcumin may be helpful when supplementing with DHA.

Bottom Line: Adults should get 250–500 mg of combined EPA and DHA daily, while children should get 4.5–5.5 mg/lb (10–12 mg/kg) of body weight.

Considerations and Adverse Effects

Vitamin D Capsules

DHA supplements are usually well tolerated, even in large doses.

However, omega-3s are generally anti-inflammatory and may thin the blood (109).

Consequently, too much omega-3 may cause blood thinning or excessive bleeding.

If you are planning surgery, you should stop supplementing with omega-3 fatty acids a week or two beforehand.

Also make sure to speak with a doctor before taking omega-3s if you have a blood clotting disorder or take blood thinning medication.

Bottom Line: Like other omega-3 fatty acids, DHA may cause blood thinning. You should avoid taking omega-3 supplements 1-2 weeks before surgery.

Take Home Message

DHA is a vital part of every cell in your body, especially the cells in your brain and eyes.

It’s also an essential part of brain development and function. What’s more, it may affect the speed and quality of communication between nerve cells.

Furthermore, DHA is important for your eyes, and it may reduce many risk factors for developing heart disease.

If you suspect you’re not getting enough in your diet, consider taking an omega-3 supplement. It is one of the few supplements that may actually be worth the money.