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Why Sunlight is Your Best Source of Vitamin D

  • November 25, 2008
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WARNING!

This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.

sunlight, sun, vitamin DA 2004 study seemed to show that vitamin D in the form of cod liver oil had only a mild effect on reducing upper respiratory tract infections in young children. This result was surprising, considering that it has been known since at least 1926 that vitamin D can significantly reduce respiratory infection, colds, and flu.

In fact, vitamin D plays a pivotal role in the immune system. The explanation likely comes from the fact that vitamin D in cod liver oil does not exist in isolation -- it comes with a high dose of vitamin A.

Vitamin A and vitamin D compete for each other’s function. For example, even the vitamin A in a single serving of liver can impair vitamin D’s rapid intestinal calcium response.

Unfortunately, Americans tend to consume multivitamins or cod liver oil that contain disproportionately small amounts of vitamin D, but detrimental quantities of vitamin A. One manufacturer sells cod liver oil containing only 3 to 60 IU of vitamin D, but between 3,000 and 6,000 IU of vitamin A.

A separate study by Daniel Hayes, Ph.D., of the New York City Department of Health and Mental Hygiene also suggests that a form of vitamin D could be one of your body's main protections against damage from low levels of radiation. Hayes explains that calcitriol, the active form of vitamin D, may protect us from background radiation and could be used as a safe protective agent before or after a low-level nuclear incident.

He points out that calcitriol is involved in cell cycle regulation and control of proliferation, cellular differentiation and communication between cells, as well as programmed cell death (apoptosis and autophagy) and antiangiogenesis.

Calcitriol is the form of vitamin D that activates your body's Vitamin D Receptor (VDR), which allows gene transcription to take place and the activation of the innate immune response.

It is possible that several of the transcriptions by the VDR will help transcribe proteins that protect the body against radiation.


Vitamin D Dose Recommendations
Age Dosage
Below 5 35 units per pound per day
Age 5 - 10 2500 units
Age 18 - 30 5000 units
Pregnant Women 5000 units
WARNING:
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.
 
Dr. Mercola's Comments:
Getting your vitamin D levels optimized is one of the most important physical strategies to stay healthy and protect yourself from numerous chronic diseases, but as this report shows all sources of vitamin D are not created equal.

Taking vitamin D in the form of cod liver oil  can be problematic if it comes along with a high dose of vitamin A, because vitamin A and vitamin D compete for each other’s function.

If you do decide to take oral vitamin D it would be best to measure your blood levels to confirm that you are receiving the correct dose, and so you can avoid overdosing on vitamin D as there are no symptoms. Once you overdose on vitamin D there is no simple way to treat it other than time and complete avoidance of vitamin D. 

Optimal Sunlight Exposure Will Give You the Right Amount of Vitamin D Every Time

Neither of these potential problems -- overdosing or competition with vitamin A -- are an issue if you get your vitamin D the way nature intended -- from the sun.

In fact, there is very little risk of overdosing on vitamin D when your body generates it from safe sun exposure. This is because when UVB light penetrates your skin, it converts a form of steroid called a sterol, the prohormone 7-dehydrocholesterol, into pre-vitamin D3. For a few days after it is created, the pre-vitamin D3 continues to undergo more changes in your skin until it becomes the actual inactivated vitamin D3.

However, if the cholesterol in your skin is exposed to the sun for long enough, then instead of becoming inactivated D3, it is converted into chemicals called lumisterol or tachysterol, which are biologically inert.

In short, this means that if you stay out in the sun for a long time, your body will produce the same amount of vitamin D that it would had you only been out for a moderate time, making it virtually impossible to overdose on vitamin D obtained from sun exposure.

Your body has a built in feedback loop that actually prevents you from overdosing on vitamin D from UVB exposure from the sun or a safe tanning bed.

When you take vitamin D orally, on the other hand, this sophisticated process that gives you just the right amount of vitamin D does not take place, leaving you vulnerable to overdose.

What to Do if You Don’t Have Access to Appropriate Sunlight

It’s important to note that while sun exposure is your best option for vitamin D, the MOST important thing is to make sure your vitamin D levels are in the optimal range (50-65 ng/ml). This means that if you do not have access to sun exposure, either because it is winter, overly cloudy or for any other reason, you need to make up for the lack of vitamin D.

One alternative option is to use a safe tanning bed (one that has the harmful emissions shielded) to have your own body produce vitamin D naturally.

The other option is to use vitamin D supplements. I am becoming more convinced of the value of vitamin D supplements, as they are less potentially toxic than I initially believed, and they are certainly more convenient and less expensive than a safe tanning bed or going to a potentially inconvenient and non-hygienic commercial tanning salon.

There are basically two types of vitamin D supplements. The natural one is D3 (cholecalciferol), which is the same vitamin D your body makes when exposed to the sun. This is the type to look for when searching for a high-quality vitamin D supplement.

The synthetic version, which is not recommended, is vitamin D2, sometimes called ergocalciferol.

Once either form of the vitamin is in your body, it needs to be converted to a more active form. Vitamin D3 is converted 500 percent faster than vitamin D2. While there have been no clinical trials to date demonstrating conclusively that D2 prevents fractures, every clinical trial of D3 has shown it does. Further, vitamin D2 has a shorter shelf life, and its metabolites bind with protein poorly, making it less effective.

Be careful, as nearly all the prescription-based supplements contain synthetic vitamin D2, which was first produced in the 1920s through ultraviolet exposure of foods. The process was patented and licensed to drug companies for use in prescription vitamins. So if you receive a prescription for vitamin D from your doctor, be aware that it is almost assuredly vitamin D2.

If you decide to take vitamin D3, how much do you need?

Well, for those in the winter with no or very limited exposure to sunshine, 4,000-5,000 units per day would seem appropriate for most adults. If you are very heavy you may need to double that dose, and for children the dose can be half that.

The key though is to make sure you monitor your vitamin D levels by blood testing to make sure your levels are therapeutic and not toxic.

I advocate getting your vitamin D levels tested regularly, but as I reported recently you now need to beware of where you’re getting your test done. For an in-depth explanation of what you MUST know before you get tested, please read my updated article Test Values and Treatment for Vitamin D Deficiency.

A Helpful Hint This Flu Season

Since flu season is upon us here in the United States, it’s worth mentioning that vitamin D levels in your blood fall to their lowest point during flu seasons. Unable to be protected by your body’s own antibiotics (antimicrobial peptides) that are released by vitamin D, if you have low vitamin D blood level you are more vulnerable to contracting colds, influenza, and other respiratory infections.

If you are getting plenty of sun exposure or taking the above doses of vitamin D, however, the odds of your getting the flu are VERY remote.

You can also use vitamin D therapeutically to TREAT the flu. The dose of vitamin D you can use would be 2,000 units per kilogram of body weight (one pound is 0.45 kg). The dose would be taken once a day for three days.

This could be a very large dose if you were very heavy (200,000-300,000 units per day), but these are the dosage recommendations that Dr. John Cannell, founder of the Vitamin D Council, has been using very successfully for a number of years.

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