ICELAND

In Iceland, a daily spoonful of cod liver oil got generations through the sunless winters.
It genuinely prevented deficiency, then got oversold as a cure for nearly everything.

Cod liver oil (lýsi)  ·  Gadus morhua  ·  Mechanism: vitamin D and omega-3

In Iceland and across the Nordic countries, cod liver oil, or lýsi, is not a trendy supplement but a fixture of ordinary daily life, a spoonful swallowed each cold, dark morning through the long winters. It is pressed from the livers of Atlantic cod, and generations of children there were raised on it as a plain matter of course.

The reason was rickets, the bone-softening disease of vitamin D deficiency that haunted sunless northern winters for centuries before anyone understood why. Cod liver oil, being unusually rich in vitamin D, quietly all but ended it, and became a lasting symbol of hardy northern health in the process ever since.

That success gave it an almost mythic reputation, the sort of thing your grandmother swore was good for absolutely everything. The trouble is that a real, specific fix slowly became a vague promise to cure whatever happened to ail you that winter.

Modern testing has since sorted the genuine from the inflated with unusual clarity for a folk remedy. What holds up is a good deal narrower than the old family legend, but what remains is solid and genuinely real.

Cod liver oil carries three active things at once: vitamin D, the omega-3 fats EPA and DHA, and a substantial dose of vitamin A. The vitamin D corrects the deficiency that causes soft, weak, aching bones, and it matters most for people who are genuinely short of it, which many are in dark winters, indoor lives, or older age, when the skin makes it far less readily.

Here the honesty has to sharpen a little. In large trials, vitamin D did not prevent fractures, heart disease, or cancer in people who already had enough of it, so it fixes a deficiency rather than working as a general tonic, while the omega-3s are the more broadly useful part, carrying solid evidence for calming inflammation, easing rheumatoid arthritis, and lowering triglycerides too.

It genuinely fixes a deficiency. It does not, it turns out, fix everything else.

There is also a real catch built into the bottle, and it is the vitamin A. Because you cannot raise the dose for more omega-3 without raising the retinol along with it, taking a lot, or stacking it with other supplements, can push vitamin A into the range that harms the liver and, ironically, thins the very bones you were trying to protect in the first place.

The how-to

Take it for the two things it truly does, correcting low vitamin D and adding omega-3s, and respect the vitamin A ceiling.

It makes the most sense if you get little sun, spend winters indoors, are older, or already know your vitamin D is low, and far less sense if you are already replete. A standard cod liver oil supplies vitamin D, omega-3s, and vitamin A together, so buy a reputable brand and read the label for the amount of each.
A common dose is a teaspoon of the liquid, or the equivalent in capsules, once a day, which gives modest vitamin D and omega-3 without overdoing the vitamin A. Do not double up to chase more omega-3, since that drags the retinol up too; if you want high-dose omega-3s, plain fish oil plus a separate vitamin D3 lets you set each one on its own.
Realistically, expect steadier vitamin D through winter, some anti-inflammatory ease for joints, and lower triglycerides, not protection from every disease. A simple blood test can tell you whether you were actually low, which is exactly when it helps most.
The main risk is too much vitamin A, so do not combine it with a multivitamin or other vitamin A supplements, and never exceed the label dose, since excess retinol can damage the liver and weaken bone. Avoid it entirely in pregnancy, because that vitamin A can harm the baby, and check with your doctor if you take a blood thinner.

Tomorrow: Russia and rhodiola
the Siberian golden root taken for fatigue and stress, and how thin the evidence really is.

See you then.