Ask a group of senior citizens about their experience with cod liver oil and you are likely to see them wrinkling their noses at the distasteful memory. People of a certain age were frequently dosed as children with cod liver oil in the winter time.
Going back hundreds of years, mothers in northern climates such as Norway, Sweden and Scotland relied on cod liver oil to keep their families healthy when the weather turned bleak. They may not have understood why this foul-tasting oily liquid seemed to be beneficial, but their powers of observation told them that children given cod liver oil were less susceptible to colds and flu.
Although this practice has fallen out of favor, scientists are now confirming that the old wives might have been on to something. Old-fashioned nasty-tasting cod liver oil contained vitamin D along with vitamin A and omega 3 fatty acids. The vitamin D might have been key against infection.
A study from Sweden just put vitamin D to a stringent test. People with impaired immunity were recruited for a year long trial (BMJ Open, Dec. 13, 2012). These people had spent at least 42 days of the prior year ill with respiratory tract infections, averaging more than four infections a year. The 140 volunteers were randomly assigned to take 4,000 IU of vitamin D3 daily or a look-alike placebo.
The results were encouraging. The researchers used a score to summarize the number of days sick, symptoms, complications and need for antibiotics. Those getting the vitamin D3 supplement had significantly lower scores on average than those on placebo.
They also needed substantially fewer antibiotics–16 days on antibiotics for those taking vitamin D3 compared to 33 days for the placebo group. Vitamin D3 was also associated with fewer ear infections, sinus infections and overall sick days, as well as secondary infections due to Streptococcus aureus and the fungi Candida and Aspergillus.
The Swedish study subjects were adults, but there have also been studies in children. Japanese investigators conducted a double-blind trial a few years ago in which schoolchildren were given 1200 IU of vitamin D3 or placebo daily for four months (American Journal of Clinical Nutrition, May 2010). The scientists were interested in how many of the youngsters came down with influenza A. In this case 10.8 percent of the children getting vitamin D caught the flu, compared to 18.6 percent of those on placebo. The vitamin-treated children also had fewer asthma attacks.
Many health professionals doubt that Americans need vitamin D supplements. But deficiency in this critical nutrient may be more common than they realize. A study of 4495 Americans revealed that more than 40 percent were seriously depleted of vitamin D (Nutrition Research, Jan., 2011).
To learn how to tell if you are low in this important nutrient and how much supplementation is optimal, you may wish to consult our Guide to Vitamin D Deficiency. It could offer a path to a healthier winter season.