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Dr Manny's Notes

Do vitamins C and D prevent the flu?

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The simple answer right now is: no.

However, I believe in vitamins C and D as essential vitamins that, at healthy levels, can slow the progression of a viral infection. But there’s no clear indication that these vitamins are preventative, and therefore, they cannot be equated to the flu shot and good hygiene.

Vitamin C was first touted as a  cold remedy in the 1970s when Dr. Linus Pauling, a Nobel laureate and biochemist, began writing how large doses of it were associated with reducing the frequency and duration of the common cold. But despite its widespread use and acceptance as a remedy of sorts, there is still very little proof as it its efficacy.

What can be said about  vitamin C, or ascorbic acid, is it’s an essential antioxidant that helps maintain muscle, bones and blood vessels. And in high doses, it seems to decrease the ability of the virus’ ability to multiply effectively at the cellular level.

Vitamin C is found naturally in many vegetables and fruits – especially citrus fruits, but it can also be found in supplement form. And whether you’re sick or not, vitamin C is vital for overall health.

The recommended daily allowance of vitamin C is 90 mg for men and 75 mg for women. And there is such thing as an “overdose” when it comes to vitamins. Taking more than 2,000 mg a day of vitamin C can result in kidney stones, nausea or diarrhea.

More and more research has come out over the years linking vitamin D deficiency to an array of health problems including heart disease, depression, rickets, cognitive impairment and even cancer.  

So it’s no surprise that vitamin D has grown in popularity among consumers for the prevention cold and flu. But again, we’re presented with the same challenges in proving that taking it can help prevent the onset of a virus.

Vitamin D is thought to play an important role in immune function, but clinical trials have shown that it is virtually powerless in the fight against cold and flu in adults with healthy levels.

A study published in the Journal of the American Medical Association, looked at 322 healthy adults in New Zealand and found that those who took large monthly doses of vitamin D developed just as many infections over an 18-month period as those who took a placebo.

Vitamin D is often referred to as the sunshine vitamin because it is produced by the body in response to sunlight, but it can also be found in some foods like fish, eggs and dairy products. But it can also be taken in supplement form.

If you have low levels of both vitamins C and D, you may be walking around with a weakened immune system, which can leave you susceptible to viral infections. But while a good balance of vitamins is essential, you must be very careful in taking mega doses of them when you’re getting sick because it may not even be worth it – and in some cases, cause more harm than good.

The bottom line is, right now, your best bet to prevent the flu is to get vaccinated.

Dr. Manny Alvarez serves as Fox News Channel's Senior Managing Editor for Health News. Prior to this position, Alvarez was a FNC medical contributor.
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