A review of a historical study from 1848 reveals that cod liver oil was an effective treatment for tuberculosis, says Professor Sir Malcolm Green in the Christmas issue published on bmj.com today.

In the study, carried out by physicians at the Hospital for Consumption, Chelsea (now the Royal Brompton Hospital), 542 patients with consumption (tuberculosis) received standard treatment with cod liver oil. These patients were compared with 535 'control' patients who received standard treatment alone (without cod liver oil).
While improvement rates were similar in the two groups, the disease was stabilised in 18% of the patients given cod liver oil, compared with only 6% of those in the control group. Deterioration or death occurred in 33% of patients given standard treatment alone, but in only 19% of those given cod liver oil, a reduction of 14%. 
Professor Green says that some children are still given cod liver oil today and perhaps this relates back to the late 19^th and early 20^th centuries when cod liver oil was widely used to treat and prevent tuberculosis. 
He adds that the steady fall in tuberculosis deaths in the late 19^th and early 20^th centuries is often attributed to better living conditions. While a reduction in overcrowded living might have reduced transmission, Green believes improved nutrition was probably as important. "It could well be that the widespread use of cod liver oil encouraged by doctors played a significant part," he writes.
Cod liver oil is a rich source of Vitamin D, which we now know is important in fighting infections, as well as preventing conditions such as rickets, says the author.
He says: "A role for vitamin D in combating tuberculosis gives a rational basis for sunshine therapy, which was widely practised for patients in sanatoriums before chemotherapy became available, as vitamin D is synthesised in the skin when exposed to the sun. Patients were put out on their beds to lie in the sun in summer and winter, and many were sent to Switzerland and other sunny countries for treatment."  He adds that today many patients who develop TB in the UK are found to be Vitamin D deficient.
Green concludes that since tuberculosis is still a common infection, accounting for millions of deaths annually across the world, there may yet be a role for vitamin D supplements in combating this terrible killer.