Denmark has received 10 Nobel Prizes in the scientific categories, five of them for physiology or medicine – a strong indicator of Denmark’s role in biomedical research from the late 19th century and through the 20th.

The first Danish Nobel Prize recipient was the physician Niels Finsen (1860–1904). In 1896, he founded the Finsen Medical Light Institute, which provided light therapy for skin diseases. With his colleagues, he constructed lamps with specialised lenses capable of focusing the light precisely on the affected skin areas.

The treatment was particularly effective against skin tuberculosis and was able to heal severe ulcers, which often affected the patients’ faces. By the early 20th century, Finsen’s light therapy was internationally known, and in 1903 he received the Nobel Prize for his work.

Finsen was a philanthropic entrepreneur, who was primarily concerned with putting his research to use for the common good. He prioritised the clinical and technical development of light therapy over more intensive basic research into the physiological mechanisms of the method.

His own health issues affected this emphasis on immediate applicability, as he suffered from chronic heart and liver disease and died the year after receiving the Nobel Prize. After Finsen’s death, his institute lived on. In cooperation with the Danish Cancer Society, it was later expanded into a cancer hospital, and in 1981 it became part of Rigshospitalet in Copenhagen. During the 1920s and 1930s, Finsen’s light therapy was gradually superseded by antibiotics and other treatments.

Denmark’s second – and perhaps best-known – physiology or medicine laureate was the zoologist and physiologist August Krogh (1874–1949). He discovered that the body’s oxygen supply is locally controlled by the smallest blood vessels, the capillaries, which open and close like tiny faucets to provide more oxygen to active muscles. His discovery of this mechanism was recognised with the Nobel Prize in 1920.

Krogh’s work mapped the mechanisms that regulate oxygen transport in the body, in particular the ability of the capillaries to adapt blood flow to the tissues’ needs. His precise physiological measurements provided a new basis for understanding respiration, metabolism and muscle performance.

Krogh’s best-known contribution is his role in introducing and producing insulin in Denmark. After visiting the Canadian researchers who had discovered the insulin hormone and proven its ability to regulate blood sugar, he made quick progress.

An important contributor in this effort was his wife, Dr Marie Krogh (1874–1943), who had diabetes and, along with her physician and colleague Hans Christian Hagedorn (1888–1971), quickly appreciated the therapeutic potential of insulin. With support from his wife, August Krogh received a licence from the researchers in Toronto to produce insulin. In 1923, the Nordisk Insulinlaboratorium (Nordic Insulin Laboratory) was founded, laying the groundwork for the company we now know as Novo Nordisk.

A later, and more controversial, Nobel Prize went to Dr. Johannes Fibiger (1867–1928). He received the 1926 Nobel Prize in Physiology or Medicine for experiments suggesting that a particular roundworm in cockroaches caused stomach cancer in rats – a finding that was considered a breakthrough at the time.

However, later studies showed that the malignant tumours were mainly due to a vitamin A deficiency in the rats. Still, Fibiger’s work was important as one of the first attempts to study cancer experimentally in a controlled laboratory environment. This approach had a significant impact on cancer research at the time and paved the way for subsequent experimental approaches.

The chemical engineer and biochemist Henrik Dam (1895–1976) was awarded the 1943 Nobel Prize in Physiology or Medicine. In experiments with putting chickens on a low-fat diet, he found that they developed haemorrhages because their blood did not clot. This led to the discovery of a previously unknown fat-soluble substance.

In 1935, Dam named this substance vitamin K, with K referring to the first letter in the Danish spelling of ‘coagulation’. Dam documented that vitamin K is needed to form prothrombin, which initiates the clotting process. His systematic dietary studies showed that a vitamin K deficiency led to internal bleeding in the chickens, thus establishing the role of vitamin K as a key factor in biochemical regulation.

Together, the Danish Nobel Prizes in Medicine or Physiology show how innovation and strong research environments have taken Denmark far. In 1984, the immunologist Niels K. Jerne (1911–1994) was the latest Dane to receive the prize in Physiology or Medicine – as the only researcher in this category who had not received direct research funding from the Carlsberg Foundation.

The chapter is written by Asser Pelle.