Cod liver oil for TB? It helped in the 19th century

By Sophie Ramsey

BMJ Group News

What do we know already?

The pungent taste of cod liver oil is familiar to many people born in the first half of the 20th century. This pale-yellow liquid, made from cod fish, was liberally used to improve health and treat a variety of ailments, including arthritis and skin wounds. Many children were also given regular doses to prevent the bone disease rickets. Rickets is caused by a lack of vitamin D, a nutrient that is plentiful in cod liver oil.

In the late 19th and early 20th century, doctors also used cod liver oil to treat tuberculosis (TB), also known as ‘consumption’. This lung infection - which is caused by bacteria - was often deadly before the discovery of antibiotics. Even today, an estimated 1.8 million people die of the disease each year, mostly in developing countries.

So did cod liver oil actually help people with TB recover - and might it play a role in TB treatment today? A fresh look at a 19th century study provides insight.

What does the new study say?

In 1848, physicians with the Hospital for Consumption and Diseases of the Chest (now the Royal Brompton Hospital in Chelsea) conducted a study involving 1,077 patients with TB. They gave 542 patients thrice-daily doses of cod liver oil in addition to their usual care, and compared them with 535 patients who had usual care alone.

The proportion of patients in each group who improved was similar: 63 percent in the cod liver oil group and 61 percent in the comparison group. However, 18 percent of those in the cod liver oil group had all or nearly all of their symptoms disappear, compared with only 6 percent in the comparison group. Also, only 19 percent of those having cod liver oil got worse or died, compared with 33 percent of those having usual care alone.

Professor Sir Malcolm Green, the researcher who revisited the study, says the high vitamin D content of cod liver oil is likely to have played a role in the differences between the groups, as we now know that vitamin D helps the immune system fight infection. This has implications for today, as research shows that many people who develop TB in the UK and elsewhere are low in vitamin D.

How reliable is the research?

The study was quite large and the patients’ health status carefully recorded. However, it was conducted long before modern standards for scientific research had been developed. So although the research was quite rigorous for its time, it does have weaknesses.

For example, the researchers didn’t describe how they decided which patients received cod liver oil. In a modern study, people would be randomly put into groups, so that researchers couldn’t consciously or unconsciously influence whether one group was healthier than the other, and more likely to recover.

Also, we can’t be certain that all the people in the study actually had TB, as laboratory tests for confirming the diagnosis had not yet been developed (indeed, the bacteria causing the disease was not recognised until 1892).

What does this mean for me?

TB is still a common and life-threatening disease in much of the world. And even with modern medicines, the disease can sometimes be difficult to treat, as some strains of TB are becoming resistant to antibiotics.

Within this context, these findings from long ago support the notion that there may be a role for vitamin D supplements (if not cod liver oil) to help combat this disease in modern times.