Omega-3 index

EPA and DHA are the two omega-3 fatty acids found mainly in oily fish: herring, mackerel, salmon, sardines. Your body hardly makes them itself, and what you take in is built into the wall of all your cells, where they keep the wall supple, dampen inflammation and play a role of their own in the heart and brain. A red blood cell lasts about four months, and the fatty acid composition of its wall is therefore an archive of what you ate in those months. The omega-3 index is the share of EPA and DHA in all the fatty acids of that wall, expressed in percent. It is a share, and that means two routes up and down: more or less EPA and DHA, but also more or less of the other fatty acids, because the division goes through the total. The index responds slowly: anyone who eats fish today sees that back only after weeks, and a change of habit shows fully after three to four months. The index is determined in red blood cells, not in the serum most blood values come from, and in the Netherlands no regular lab measures it; anyone who has it had it done at a foreign or non-certified laboratory. So there is no normal; what there is, is a target range of 8 to 12 % from research on the heart and vessels, with below 4 % as undesirable. Anyone who eats little fish usually sits around 4 %.

Unlike most nutritional values in blood, this index gives an average over months instead of a snapshot. That is why it exists: a fatty acid in the serum moves with your last meal, the share in the cell wall with your habit. Anyone who wants to know whether they take in enough omega-3 gets the most honest answer here. The second reason is the link with the heart and vessels. In large population studies people with a high index had less chance of sudden cardiac death and of cardiovascular disease in general, and the target range of 8 to 12 % comes from that work. EPA and DHA lower the triglycerides, keep the heartbeat more regular and dampen inflammation in the vessel wall. Two portions of oily fish a week is what the Dutch dietary guidelines recommend for that reason. The honest limitation is that the index is mainly a research measure. In the Netherlands nobody measures it, the author who published the target range has interests in a laboratory that offers the test, and the studies of fish oil as a supplement show smaller effects than those of fish in the diet. So read the index as a measure of your fish intake over months, and leave the question of whether your heart is healthy to your blood pressure, LDL, triglycerides and fitness.

A low index means there is little EPA and DHA in your cell walls. Usually it is the first and rarely the last: little oily fish in your diet, because your body hardly makes these fatty acids itself and one portion a month is too little to fill the wall; and more of the other fatty acids, especially the omega-6 fatty acids from sunflower oil and processed food, which take up the place in the wall and lower the share without less omega-3 having come in. Anyone who eats little fish usually sits around 4 %, and that is the undesirable side. A high index means a lot of EPA and DHA in the wall, and that is the favourable side: more oily fish or fish oil in your diet, because the wall fills over months with what you take in, and less of the other fatty acids, so the share rises without more omega-3 having come in. Above 12 % the research says nothing more; there is no upper limit with a published meaning, but there is also no reason to aim higher. The index belongs beside your triglycerides, which fall with more EPA and DHA, beside your HDL and LDL, which the question of your vascular risk works on, and beside your previous index from the same laboratory, because the measurement is not standardised and the value changes slowly.