Vitamin C has been used for the prevention of colds for decades, but little scientific evidence supports its effectiveness. In contrast, evidence has accumulated that vitamin D plays a key role in the immune system.
The wintertime deficiency of vitamin D, which the body produces in response to sunlight, has been implicated in the seasonal increase in colds and flu, and previous small studies have suggested an association between low blood levels of vitamin D and a higher risk of respiratory infections.
The newest study analyzed blood levels of vitamin D from almost 19,000 adult and adolescents, selected to be representative of the overall U.S. population.
|Vitamin D Dose Recommendations|
|Below 5||35 units per pound per day|
|Age 5 - 10||2500 units|
|Pregnant Women||5000 units|
There is no way to know if the above recommendations are correct. The ONLY way to know is to test your blood. You might need 4-5 times the amount recommended above. Ideally your blood level of 25 OH D should be 60ng/ml.
It’s exciting to see such a large-scale study confirm the previous findings by Dr. John Cannell, founder of the Vitamin D Council. He first introduced the hypothesis that influenza is merely a symptom of vitamin D deficiency in the paper Epidemic Influenza and Vitamin D, published in the journal Epidemiology and Infection two years ago, followed up with another study published in the Virology Journal last year.
This latest study is the largest and most nationally representative of its kind to date, involving about 19,000 Americans. In conclusion, lead author Dr. Adit Ginde stated:
"The findings of our study support an important role for vitamin D in prevention of common respiratory infections, such as colds and the flu. Individuals with common lung diseases, such as asthma or emphysema, may be particularly susceptible to respiratory infections from vitamin D deficiency."
There are several other studies supporting the role of vitamin D in prevention of common respiratory infections. At least five studies show an inverse association between lower respiratory tract infections and 25(OH)D levels. That is, the higher your vitamin D level, the lower your risk of contracting colds, flu, and other respiratory tract infections:
1. A 2007 study suggests higher vitamin D status enhances your immunity to microbial infections. They found that subjects with vitamin D deficiency had significantly more days of absence from work due to respiratory infection than did control subjects.
2. A 2009 study on vitamin D deficiency in newborns with acute lower respiratory infection (ALRI) confirmed a strong, positive correlation between newborns’ and mother’s vitamin D levels. Over 87 percent of all newborns and over 67 percent of all mothers had vitamin D levels lower than 20 ng/ml, which is a severe deficiency state.
Newborns with vitamin D deficiency appear to have an increased risk of developing ALRI, and since the child’s vitamin D level strongly correlates with its mother’s, the researchers recommend that all mothers’ optimize their vitamin D levels during pregnancy, especially in the winter months, to safeguard their baby’s health.
3. A similar Indian study published in 2004 also reported that vitamin D deficiency in infants significantly raised their odds ratio for having severe ALRI.
4. A 2009 analysis of the Third National Health andNutrition Examination Survey examined the association between vitamin D levels and recent upper respiratory tract infection (URTI) in nearly 19,000 subjects over the age of 12.
Recent URTI was reported by:
- 17 percent of participants with vitamin D levels of 30ng/ml or higher
- 20 percent of participants with vitamin D levels between 10-30 ng/ml.
- 24 percent of participants with vitamin D levels below 10ng/ml
The positive correlation between lower vitamin D levels and increased risk of URTI was even stronger in individuals with asthma and chronic obstructive pulmonary disease.
5. Another 2009 report in the journal Pediatric Researchstated that infants and children appear more susceptible to viral rather than bacterial infections when deficient in vitamin D. And that, based on the available evidence showing a strong connection between vitamin D, infections, and immune function in children, vitamin D supplementation may be a valuable therapy in pediatric medicine.
What is a Healthy Vitamin D Level?
In the United States, the late winter average vitamin D level is only about 15-18 ng/ml, which is considered a very serious deficiency state. It’s estimated that over 95 percent of U.S. senior citizens may be deficient, along with 85 percent of the American public.
It’s not so surprising then that the average American adult typically gets two colds per year. And those who are seriously deficient may suffer at least one additional one. But that’s under the current, now outdated, guidelines for normal vitamin D levels. I strongly believe you could avoid colds and influenza entirely by maintaining your vitamin D level in the optimal range.
In this study, the median serum 25(OH)D level was 29 ng/mL, which is just below what’s considered “normal.” Actually, the author of the article in Scientific American above got this one wrong, stating 30 ng/mL was considered “optimal.” It is not.
It’s important to realize that what’s conventionally considered normal is NOT the same as optimal.
Some experts may disagree with the latest vitamin D ranges below, but they are derived from large-scale clinical research findings, based on healthy people in tropical or subtropical parts of the world who receive healthy sun exposures. It seems more than reasonable to assume that these values are in fact reflective of your optimal requirements.
In this latest study, those whose vitamin D levels were below 10 ng/mL had a 36 percent greater risk of getting a cold, and those with levels between 10-30 ng/mL experienced a 24 percent greater risk compared with participants whose levels were at least 30 ng/mL.
Those with asthma who were also deficient in vitamin D were five times more likely to get sick than asthmatics with normal levels.
However, if you were to maintain your vitamin D levels within the optimal range shown above, you would likely avoid being affected during the cold and flu season entirely.
How Do You Know if You’re Deficient?
I believe it’s imperative that you have your vitamin D levels checked on a regular basis, to make sure you’re maintaining optimal levels.
This is not as important if you’re getting your vitamin D from appropriate sun exposure during the summer months, as your body will not overdose on vitamin D created through tanning. However, always get your levels tested if you are taking an oral vitamin D supplement.
It is typically not necessary to do this before you start taking vitamin D but you should do it after a few weeks to a month to confirm what your level is and make sure that you are taking the correct dose.
The one caution here in the US is to be certain your test is performed at a lab like Labcorp, that uses the gold standard Diasorin test for checking vitamin D levels.
For an in-depth explanation of everything you need to know before you get tested, please read my latest updates in Test Values and Treatment for Vitamin D Deficiency.
Government Recommendations for Vitamin D Levels May Soon Change
The most recent recommendations from the Institute of Medicine (IOM), which are 12 years old, recommend only 200-600 IU’s of vitamin D per day. But it’s important to realize that these recommendations were based on the vitamin D's impact on bone health, not immunity, cancer protection, or overall health.
Fortunately, due to the recent landslide of excellent vitamin D studies, the IOM is expected to review and revise their recommendation in May 2010. That’s still a ways out though, and I strongly suggest you don’t wait until then to take another look at your vitamin D status.
Likewise, the American Academy of Pediatrics recently doubled its recommended dose of vitamin D for children. Unfortunately this is still a woefully inadequate recommendation as the dose should be TEN times larger. Rather than going from 200 to 400 units per day, it should have increased to about 2,000 units per day.
And for adults, the appropriate dose would likely be closer to 4,000-5,000 units per day, but it could be even higher. In fact, according to Dr. Heaney, your body requires 4,000 IU’s daily just to maintain its current vitamin D level. So in order to actually raise your levels, you’d have to increase either your exposure to sunshine, or supplement with oral vitamin D3 (which I do not recommend without having your levels tested first).
One thing is clear. By maintaining optimal vitamin D levels, you will help prevent not only colds and flu, but all manner of disease, and maintain good health.
For a great overview of the nearly unbelievable health benefits of this vitamin, I strongly recommend you watch my one-hour free vitamin D lecture.