Preventing Colds By Optimizing Your Vitamin D Levels

More and more evidence is accumulating showing that vitamin D is playing a key role in the immune system. There are several studies supporting the role of vitamin D in prevention of common respiratory infections. One of the largest studies (Ginde et al., 2009) showed that people with the lowest blood vitamin D levels reported having significantly more recent colds or cases of the flu. And that the risks were even higher for people with chronic respiratory disorders such as asthma.

What is vitamin D

Vitamin D is not really a vitamin but a group of fat-soluble prohormones. There are several forms of vitamin D but the two most relevant to humans are vitamins D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D2 is produced by some organisms of phytoplankton, invertebrates and fungi in response to UV irradiation.  Vitamin D3 is produced in the skin of vertebrates after exposure to ultraviolet B light from the sun. Vitamin D3 also naturally occurs in fish and few other foods.

Supplemental vitamin D is either vitamin D3 or vitamin D2. Nowadays vitamin D3 is preferred as supplement since it is the same substance as what is produced in human skin in response to sun exposure. Supplemental D3 is derived either from lanolin or cod liver oil extract.

Healthy vitamin D level

Vitamin D status is determined by measuring serums concentration of 25-hydroxy-vitamin D (also known as 25(OH)D or calcidiol). It reflects to vitamin D produced in skin as well as that acquired from the diet. A concentration above 15ng/ml (37,5 nmol/l) is commonly considered adequate for those in good health while levels above 30ng/ml (75nmol/l) are proposed desirable for achieving optimum health.

However recent studies have shown that level that is conventionally considered as normal is not the same as optimal. According to latest research findings it seems very reasonable to assume that values below are in fact more reflective to optimal requirements:

deficient: <50ng/ml (<125nmol/l

optimal: 50-70ng/ml (125-175nmol/l)

treat cancer and heart disease: 70-100ng/ml (175-250nmol/l)

excess: >100ng/ml (250nmol/l)

In the United States the late winter average vitamin D level is only about 15-18ng/ml (=37,5-45 nmol/l). This can already be considered as serious deficiency state. It is also estimated that 40-60% of global population is at risk for vitamin D deficiency.

How to get your vitamin D

There are two ways to receive vitamin D in the amounts needed for proper health: sun (UVB) exposure and vitamin D supplementation.

Sun exposure should be the number one method of choice for getting vitamin D. Studies have shown that large quantities (approx. 10000IU) of vitamin D are synthesized in the skin in response to full-body summer sun exposure. However the dosing of sun exposure is a bit complex since it is dependent on skin color and involves knowing the amount of UVB present. Couple rule of thumbs:

  • for vitamin D production sun exposure should be midday between hours of approx. 10am-2pm
  • person with white skin will need around 15 minutes of full body sun exposure whereas those with dark skin will need 3-6 times longer exposure
  • exposure beyond minimal dose required to produce skin redness does not increase your vitamin D production any further, because when equilibrium is reached in the skin,  the ultraviolet light will start to degrade the vitamin D
  • sunburn has no health benefits
  • if your shadow is longer than you are , you are not making much vitamin D
  • occasional exposure of your face and hands to sunlight is NOT sufficient for vitamin D nutrition
  • if your latitude is above 30 degrees north or below 30 degrees south you will likely need vitamin D supplementation roughly from September to mid-April

If vitamin D is obtained from the sun it is not necessary to get vitamin D levels tested as the body will not overdose on vitamin D created trough tanning. However when taken orally in supplement form vitamin D levels should always be checked to make sure that correct dose is being taken. Vitamin D level testing is best to be done after a few weeks to a month from starting the supplementation.

Vitamin D potency is measured in International Units (IU) – one IU equaling to 0.000025 milligrams (mg). Also micrograms (mcg or µg) are commonly used – 40IU equaling to one microgram. Official recommendations for vitamin D intake usually vary between 400 to 1000IU, depending of country. While these amounts are sufficient to maintain bone health and normal calcium metabolism in healthy people, they are found to be inadequate to raise and/or maintain the vitamin D levels necessary for proper health. For proper functioning, a healthy human body utilizes around 4000 IU of vitamin D per day. Thus the appropriate dose for adult would be closer to 4000-5000 IU per day. As an example, based on body’s indicated daily vitamin D usage, Vitamin D council recommends following amounts of supplemental vitamin D3 in the absence of proper sun exposure.

  • Healthy children under the age of 1 years – 1000 IU
  • Healthy children over the age of 1 years – 1000 IU per every 25lbs (11,3kg) of body weight
  • Healthy adults and adolescents – at least 5000 IU
  • Pregnant and lactating mothers – at least 6000 IU


It is clear that by maintaining optimal vitamin D levels you can help prevent not only colds and flu, but all manner of disease, and maintain good health altogether. Sunlight should be the number one source for vitamin D but it is crucial to avoid sunburn. Before considering supplementation with vitamin D it is wise to get vitamin level tested, preferably with nutritionally oriented physician.

Back to Top3

Back to remedies