Grandmothers in Scandinavia have been forcing children to swallow cod liver oil for hundreds of years. They knew it acted as a tonic in the winter to keep colds and other upper respiratory tract infections away. A meta-analysis published in the BMJ (Feb. 15, 2017) confirms that the old wives were right: The answer to the question is vitamin D good for colds is yes.
Many Physicians Pooh-Pooh Vitamins:
Many health professionals believe that people should not take vitamins. A few years ago an editorial in the Annals of Internal Medicine (Dec. 17, 2013) stated this message in words no one could misunderstand:
“Enough is Enough:
Stop Wasting Money on Vitamin and Mineral Supplements.”
Many doctors take that advice to heart. They tell their patients to skip nutritional supplements and just eat a well balanced diet, whatever the heck that means. At the same time Americans are told to skip vitamins, they are told by their dermatologists to slather on the sunscreen to prevent sun damage. Sunscreen blocks the body’s ability to make vitamin D in the skin.
Vitamin D Deficiency is Common:
The result is that massive numbers of U.S. citizens are low in this crucial hormone. According to the CDC Second National Report on Biochemical Indicators of Diet and Nutrition, nearly 70 million people are below optimal levels (under 20 ng/mL). Over 20 million Americans are deficient in Vitamin D (below 12 ng/mL).
Vitamin D and Immunity:
Ask a room full of senior citizens if they remember getting a spoonful of cod liver oil in the winter time when they were children and a bunch of hands will shoot up. That is almost always accompanied by a grimace. That’s because people remember the awful taste of that cod liver oil.
Why did mothers dose up their kids with such foul-tasting stuff for six months of the year? They could not tell you how it worked, but experience taught them that it did. Over the last decade or two a number of studies have suggested that at least one of the ingredients in cod liver oil probably boosted immunity and reduced the likelihood of getting sick. The most likely factor: vitamin D.
Is Vitamin D Good for Colds?
The study in the BMJ set out to “assess the overall effect of vitamin D supplementation on risk of acute respiratory tract infection, and to identify factors modifying this effect.” The authors analyzed 25 randomized controlled trials involving over 11,000 subjects “aged 0 to 95 years.”
The Conclusions:
“Vitamin D supplementation was safe and it protected against acute respiratory tract infection overall. Patients who were very vitamin D deficient and those not receiving bolus doses experienced the most benefit.”
What’s a “Bolus” Dose?
When doctors refer to the administration of a “bolus” dose they usually mean a big dose all at once. An example would be an intravenous injection of a medication at a fairly rapid rate. It is a way of getting a large amount of medicine into a patient quickly, especially during an emergency. But a bolus dose is not always injected. Sometimes doctors prescribe large doses of oral medication.
For reasons that confuse us, some doctors like to prescribe a large dose of vitamin D weekly or monthly instead of daily. For example, a number of studies report on protocols involving 100,000 IUs (international units) of vitamin D2 taken orally every three months. Other trials have used single doses of 300,000 to 500,000 IUs.
No grandmother in Sweden or Norway would have considered such a whopping dose sensible. They intuitively realized that small daily doses were more physiologic.
Is Vitamin D Effective?
Many people ask us: is vitamin D good for colds? Until now we had to be cautious in our answer. That’s because the results of various studies have been equivocal. Meta-analyses of 15 clinical trials have come to conflicting conclusions. Two such reviews responded favorably to the question is vitamin D good for colds and three replied negatively to that question. The new analysis drilled deeper for an answer we think is more robust.
The authors wanted to know why there was such variability in the conclusions of different vitamin D studies. They analyzed baseline vitamin D status, dosing frequency, other conditions (asthma, COPD), vaccine status, etc. What they found was that using daily or weekly vitamin D dosing:
“revealed a protective effect against acute respiratory tract infection. No such protective effect was seen among participants in trials where at least one bolus dose of vitamin D was administered.”
In other words, taking a large oral dose of vitamin D once a month or once every three months was ineffective at warding off colds or flu. The researchers dug even deeper. They wanted what they described as a “cleaner” look at the data. They found that people who had very low levels of vitamin D at the beginning of the trial experienced “an even greater degree of protection against acute respiratory infection.”
The Bottom Line in Answering the Q: “Is Vitamin D Good for Colds?
The authors 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.”
Many health professionals will likely find fault with the latest meta analysis. The idea that the old wives might have been right makes some physicians uncomfortable. An editorial that accompanied the BMJ research article was titled: “Do Vitamin D Supplements Help Prevent Respiratory Tract Infections?”
The authors were not enthusiastic:
“Should these results change clinical practice? Probably not. The results are heterogeneous and not sufficiently applicable to the general population. We think that they should be viewed as hypothesis generating only, requiring confirmation in well designed adequately powered randomised controlled trials…We consider that current evidence does not support the use of vitamin D supplementation to prevent disease, except for those at high risk of osteomalacia [weakened bones], currently defined as 25-hydroxyvitamin D levels less than 25 nmol/L.”
Despite this conclusion, we think that vitamin D supplementation, especially in the winter, makes sense for a lot of people. Anyone with dark skin is at higher risk of vitamin D deficiency. People who stay out of the sun or slather on the sunscreen will also be vulnerable. And those who live in northern states where sun is at a premium for many months of the year will also be at risk of low vitamin D levels. The authors of the Vitamin D study concluded that: “Use of vitamin D did not influence risk of serious adverse events of any cause or death due to any cause.” In other words, vitamin D was safe.
Want to Learn More?
Our Guide to vitamin D Deficiency will provide you an in-depth understanding of this crucial nutrient. Learn about symptoms of low vitamin D levels. Find out what the blood tests reveal and how much vitamin D is appropriate. Which forms of vitamin D are best? Here is a link to all our guides.
