DHA and EPA Explained: How to Choose a Japanese Fish Oil Supplement

Japan was the first country to turn a fish oil fraction into a prescription drug, and a supermarket supplement there may say on the box that it helps maintain memory. The shelf is unusually specific about what it is selling, once you know the vocabulary.

Two fatty acids matter: DHA and EPA. Most products contain both, but the ratio decides what the bottle is for, and the dose decides whether it is likely to do anything.

Here is the difference, the numbers, and the problem the front label never mentions: fish oil goes off.

DHA and EPA do different jobs

Both are long-chain omega-3 fatty acids, made by algae and concentrated up the food chain into oily fish. The body converts a little from plant omega-3 (the ALA in flax or perilla oil), but typically under 10% for EPA and far less for DHA, which is why fish oil is the practical source.

Name	Japanese	Where it concentrates	What the evidence broadly supports
DHA	ドコサヘキサエン酸 (docosahexaenoic acid)	Brain, retina, nerves	Structural fat of neural membranes; modest support for memory maintenance in older adults
EPA	エイコサペンタエン酸 (eicosapentaenoic acid)	Blood and cell membranes	Lowers blood triglycerides at gram doses; the fraction used in Japanese cardiovascular prescriptions

If your interest is memory or eyes, weight the bottle towards DHA; if it is triglycerides, weight it towards EPA. A mixed product is fine for general use, and most Japanese formulations lean DHA because that is what the memory claim rests on.

The archetypal Japanese DHA product: 510 mg of DHA and 110 mg of EPA across four softgels, carrying both the memory and triglyceride claims.

Why Japan eats so much and still buys the capsules

The Japanese diet has historically delivered around a gram of EPA and DHA a day from grilled mackerel, sardines and raw fish, and Japan's dietary reference intakes have long pointed at roughly 1 g a day as a target. The habit is fading: per-capita fish consumption has fallen by close to half since its 2001 peak, and the supplement market grew up in that gap, aimed at people who know they should eat blue fish (青魚, aozakana) twice a week and do not.

A pared-back option: 270 mg of EPA plus DHA in one small capsule, meant to top up a fish-free week rather than treat anything.

What the label is allowed to say

Most fish oil claims sit under 機能性表示食品 (kinōsei hyōji shokuhin, food with functional claims): the maker notifies the Consumer Affairs Agency with a review of published evidence for the ingredient at the stated dose. It is a notification, not an approval.

For DHA and EPA the notified wordings are that they "help maintain memory that tends to decline with age" and "help reduce triglycerides in the blood". Both rest on real trials, but the memory effect is modest and clearest in older adults with low baseline intake. Read the claim as supported, not promised.

The other common positioning: an EPA-and-DHA product notified specifically for neutral fat (中性脂肪, chūsei shibō, the Japanese term for triglycerides), aimed at people whose annual health check flagged the number.

How much to take

1. General maintenance: 250–500 mg of combined EPA and DHA a day, the range most international bodies cite for adults who do not eat oily fish. Many Japanese products sit here.
2. Memory claims: notified doses are usually 300–600 mg of DHA a day.
3. Triglyceride lowering: reliable at 2–4 g a day, which is prescription territory. Japan's EPA drug has been dosed at 1.8 g a day since 1990. Doses this high belong under a doctor's supervision.

Count the omega-3s, not the oil: a 1,000 mg capsule may hold 300 mg of EPA and DHA. Japanese labels usually state the fatty-acid content per daily serving.

At 860 mg of EPA and DHA per serving this is one of the higher-dose shelf products, between a maintenance dose and the level at which triglyceride effects begin.

Triglyceride form or ethyl ester

Fish oil exists naturally as triglycerides. To concentrate it, makers convert it to ethyl esters and distil off unwanted fats; some convert it back into re-esterified triglycerides. Ethyl esters absorb noticeably less well on an empty stomach, triglyceride-form oil absorbs well either way. Most Japanese packs do not state the form; 精製 (seisei, refined) on the label suggests a concentrate.

Whatever the form, take fish oil with the largest meal of the day. It roughly doubles absorption of ethyl esters and reduces the fishy reflux that puts people off.

Oxidation and storage

Polyunsaturated fats oxidise easily. Rancid oil loses its benefit and may do mild harm, and the industry's peroxide values never appear on a consumer pack.

• Buy 30 to 60 days' worth, not a year's supply.
• Keep the sealed bottle cool and dark; refrigerate after opening.
• Bite one capsule from a new bottle. A faint sea smell is normal; a sharp, paint-like note means it has turned.
• Vitamin E (ビタミンE) on the ingredients list is there as an antioxidant.

Sardine, anchovy, cod liver and krill

Most Japanese fish oil comes from small, short-lived fish (sardine, anchovy, mackerel), whose size keeps mercury low before the oil is distilled anyway.

A straightforward blue-fish oil giving 400 mg of omega-3 in two capsules: a reasonable first bottle for someone who simply wants the fish they are not eating.

Cod liver oil is pressed from the liver, not the flesh, and carries substantial vitamin A and D alongside its omega-3s. That makes it unsuitable for stacking with a separate vitamin A supplement or for pregnancy.

Hand-extracted from Hokkaido cod, this is the traditional version: an omega-3 source that is also a vitamin A and D supplement, so count it as both.

Krill oil carries omega-3s as phospholipids with a little astaxanthin, which helps absorption and oxidation resistance, but each capsule holds far less EPA and DHA and it is a shellfish product.

Who should be careful

• Anticoagulants and antiplatelets. Fish oil mildly thins the blood. On warfarin, DOACs or daily aspirin, tell the prescriber before taking more than 1 g a day.
• Pregnancy. DHA is recommended, but choose fish-body oil rather than cod liver oil because of the vitamin A.
• Atrial fibrillation. Gram-level doses in recent trials showed a small rise in AF.

Frequently asked questions

Is DHA or EPA better? Neither in the abstract. DHA is the structural fat of the brain and retina; EPA has the clearest effect on triglycerides.

Do I need it if I eat fish twice a week? Probably not. Two portions of oily fish deliver roughly the maintenance dose the supplements aim for.

Why do the capsules repeat on me? An empty stomach or a bottle that has started to oxidise. Take them with a meal and keep them cold.

Is algae oil as good? It supplies DHA well and some EPA, and is the right choice for vegetarians; the dose per capsule is often lower.

Fish oil is a quiet supplement: the right dose, with food, from a bottle that has not gone off. The supplement routine guide covers how to sequence it, and the joint support guide picks up where omega-3s overlap with glucosamine.