Low vitamin D means more flu

Did you ever wonder why you end up suffering from the flu nearly every winter? You may not be getting enough vitamin D.

The darker winter months are when our sun-dependent vitamin D levels are at their lowest.

Among its many other actions, vitamin D stimulates and supports immune function. And in temperate latitudes, researchers find that pandemic influenzas generally show clear seasonality.

In other words: More cold dark days, more flu.

Growing research connects vitamin D and influenza

  • Women given 800 IU of vitamin D daily were 3 times less likely to report cold and flu symptoms than those not given vitamin D. This study was a randomized controlled trial looking at bone loss in postmenopausal African American women.
  • A study with intake of 2,000 IU of vitamin D daily for one year efficiently protected women against typical winter colds and influenza.
  • A trial comparing vitamin D supplements with placebos in schoolchildren found that only 1,200 IU per day of vitamin D during winter and early spring reduced the incidence of seasonal influenza by a factor of two.

Protect yourself from winter flu related to low vitamin D

  • Maintain a 50 to 60 ng/ml vitamin D level all year round to get the fullest possible benefits from vitamin D.
  • Get your vitamin D tested now to prepare for the winter. To get your level to the optimal 50 to 60 ng/ml some may require the intake of 4,000 to 5,000 IU daily of vitamin D or even more. For others lesser doses are sufficient. Some people absorb vitamin D better than others, some seem to have a higher need and others have higher reserves from the summer.
  • Determine how much extra D you need. As a rule of thumb, for every 1,000 IU increase in vitamin D your vitamin D blood level will increase by 10 ng/ml. So if you measure your level in December and it is 30 ng/ml, you would add 2,000 IU more vitamin D to your daily supplement program to get to a 50 ng/ml.

Here’s to a happy, healthy winter season!



Cauley JA, Chlebowski RT, Wactawski-Wende J, et al. Calcium plus vitamin D supplementation and health outcomes 5 years after active intervention ended: the Women’s Health Initiative. J Women’s Health (Larchmt). 2013;22:915-929.

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