Avoiding colds and flu is challenging. Physicians will tell you that vaccination is the only protection against influenza. Frequent hand washing is the other standard recommendation.
Unfortunately, immunization is imperfect. The CDC reports that this year’s flu shot is about 48 percent effective overall. Hand washing is important, but it does not protect you from someone’s cough or sneeze launching airborne viral particles in your direction, resulting in colds or flu.
Cod Liver Oil Against Colds:
There is another option. Mothers have been dosing their families with cod liver oil for hundreds of years. Although they never performed double-blind, placebo-controlled trials, they were convinced that this “tonic” offered some protection from upper respiratory infections.
Now scientists have figured out how cod liver oil might have helped. This fish product is rich in vitamin D.
Boosting Vitamin D to Prevent Colds and Respiratory Infections:
A study in the BMJ (Feb. 15, 2017) suggests that vitamin D supplements can boost resistance to respiratory infections. The investigators analyzed 25 randomized controlled trials with more than 11,000 volunteers. What they found upon analysis is that vitamin D was most beneficial for those who had low blood levels of 25-hydroxyvitamin D at the outset.
The scientists also detected much greater protection against respiratory viruses among those who took their vitamin D supplement every day instead of once a month or once every few months (a “bolus” dose). They conclude:
“Our study reports a major new indication for vitamin D supplementation: the prevention of acute respiratory tract infection. We also show that people who are very deficient in vitamin D and those receiving daily or weekly supplementation without additional bolus doses experienced particular benefit.”
Who Might Benefit from Vitamin D Supplements?
How many people might be low enough in vitamin D to benefit from supplements? The CDC Second National Report on Biochemical Indicators of Diet and Nutrition found that almost 70 million Americans had 25-hydroxyvitamin D levels below the optimum (at least 20 ng/mL). In fact, more than 20 million tested below 12 ng/mL, a level that signals frank deficiency.
Why is vitamin D insufficiency so common? Sun exposure is the primary source for vitamin D. With concerns about skin cancer, people are covering up more, avoiding the sun and slathering on the sunscreen. This reduces the amount of vitamin D their bodies make during the summer.
In the winter, people in northern regions make little, if any, vitamin D. That’s why mothers in northern climates gave their families cod liver oil in the winter, even though they did not understand the reason it worked.
Learning More About Vitamin D:
If you would like to know more about this critical nutrient that functions as a hormone in the body, we invite you to read our Guide to Vitamin D Deficiency. Many physicians still believe that Americans don’t need supplements if they eat a well-balanced diet. Very few diets provide adequate levels of vitamin D, however. Consequently, people should have their level of 25-hydroxyvitamin D checked to see if it is adequate, especially during cold season.