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← All research storiesNorway, 1940–1945

A Wartime Natural Experiment

During the WWII occupation of Norway, the national diet changed and so did deaths from circulatory disease. A fascinating natural experiment — and a heavily confounded one.

Historical Natural ExperimentObservational
Pre-1940Higher circulatory-disease deaths
1940–1945 occupationAnimal-fat availability drops · circulatory deaths fall
Post-1945Diet rebounds · deaths rise again
Schematic of the pattern described by Strøm & Jensen (1951) — direction only, not data values, and not a reproduction of any published figure.

What happened

Writing in The Lancet in 1951, Strøm and Jensen reported that deaths from circulatory diseases in Norway fell during the 1940–1945 occupation — a period when the availability of animal fats dropped sharply — and rose again after the war. Contemporaries described broadly similar wartime patterns in other occupied or blockaded European countries.

Why it's interesting

The post-war rebound strengthens the temporal link: the decline tracked with the years of restricted food supply and reversed when conditions changed. That kind of before-during-after pattern is what makes natural experiments worth a careful look.

What it suggests

  • Large, population-wide reductions in animal-fat intake can coincide with lower cardiovascular mortality.

What it does not prove

  • Wartime changed many things at once — overall food scarcity, far more walking, cycling, and manual labor, less tobacco and alcohol, and fewer processed or sugary foods.
  • Death certification, diagnosis, and competing causes of death also shifted during the war, so the measured decline is not clean evidence that removing animal foods caused it.

We deliberately avoid dramatic framings like 'the occupiers took all the livestock.' The credible record is an observed mortality pattern during a period of food-supply change — not a single, simple cause.

The takeaway

A natural experiment is a strong hint with weak controls: genuinely fascinating, genuinely confounded, and not proof on its own.

Sources & citations (3)Tap to open
  1. Mortality from circulatory diseases in Norway 1940–1945
    Strøm A, Jensen RA · The Lancet 257(6647):126–129 · 1951
  2. Paul Owren, Christopher Bjerkelund and the dawn of controlled trials in Norway (notes wartime decline in heart attacks)
    The James Lind Library
  3. Wartime mortality and pathology (CVD epidemiology history archive)
    University of Minnesota, Division of Epidemiology
    Secondary academic resource. Re-confirm the live URL before relying on it — the host's certificate was misconfigured at time of research.

We summarize these sources in our own words and link to the originals. Summaries can simplify nuanced findings — follow the links for the full picture.