Results from vitamin D trials are not always positive. One important aspect to consider when looking at any vitamin D trial is the frequency of dosing. Were supplements given daily, weekly, monthly, yearly? Instead of giving vitamin D daily, which is hard to monitor for every subject, it is not uncommon to give subjects a larger dose less frequently. The idea is that if you want to give the equivalent of 1,000 IU/day – then it is easier to manage by giving 30,000 IU once a month.

But does this work? Can 30,000 IU/month provide the same benefit as 1,000 IU/day? Would one day of extreme sunbathing be the same as daily exposure of 20-30 minutes?

Let’s understand the science behind how vitamin D works in your body.

What is a half-life?

Important to understanding how vitamin D is processed in your body is the concept of a half-life. The half-life of a compound, vitamin D in this case, is a time measurement of how long that compound remains in the body. It is the amount of time in which half of the substance is gone. Then, when that amount of time passes again, another half of what remained previously is gone. So, it is exponential in nature. The graph looks like this:

Source: Chemistry LibreTexts

How is vitamin D absorbed and used in your body?

Vitamin D is produced in or enters the body through sun exposure, diet or a supplement and goes into the blood stream where much of it binds to the vitamin D binding protein (VDBP) – a protein that carries vitamin D compounds into circulation. From there, vitamin D functions within both the endocrine system and the autocrine/paracrine system.

#1 – The Endocrine System – for skeletal health

Until recently, most research about vitamin D has revolved around the endocrine system which maintains bone health. Vitamin D, from UV exposure or diet, is delivered to the liver, converted to 25-hydroxyvitamin D, or 25(OH)D, and moved into circulation where it has a half-life of approximately three weeks.

As necessary, 25(OH)D is then transferred to the kidney where it is further converted to the active form of 1,25(OH)2D which has a half-life of only a few hours. This active form helps to control calcium absorption and bone health. All the successful studies on vitamin D and bone health have benefited from the long half-life and availability of 25(OH)D. For bone health, the important thing is the amount of 25(OH)D available, rather than direct intake of vitamin D.

Because of the three-week half-life, there is not a large difference between dosing every week, every 2 weeks, or 3 weeks. So, if we were only concerned about our skeletal system we could take vitamin D only once a month and it should provide benefits to bone health, but do we want more than that?

#2 – The Autocrine/Paracrine System – for autoimmune health

What has not been appreciated until relatively recently is that in addition to being delivered to the liver for conversion to 25(OH)D, vitamin D is also delivered directly to all tissues of the body. Many of these tissues, such as breast, colon, prostate, and brain, can convert vitamin D to its active form within the tissue. It is through this process that vitamin D can help enable the cells to fight against infections, disease, and autoimmune disorders.

Vitamin D3 has a half-life in the autocrine system of roughly 24 hours, so in order for it to have a meaningful impact on cellular functions, you need a new supply of it every day. This understanding means that frequency of dosing matters when testing for disease reduction and immune control – large monthly or quarterly doses that are effective for bone health are not likely to show positive results for disease reduction. For disease prevention and treatment, daily dosing (food, sun, and supplement) is very important!

Why does this matter for clinical trials?

Most of the clinical trials conducted in the past 40 years have focused on the endocrine system and have consistently shown the positive effects of vitamin D on bone health regardless of dosing regimen (from daily to quarterly). In the past 10 years, many new clinical trials have focused on nonskeletal outcomes such as autoimmune disorders, cancer, cardiovascular disease, and infections. These new studies have also used various dosing regimens, but have yielded inconsistent results. Those with adequate daily vitamin D inputs have largely shown positive results while many of those with longer dosing intervals have shown no vitamin D effect. While 25(OH)D levels are maintained in these studies, it is the vitamin D3 levels that are essential to these systems. Therefore, it is necessary to design a clinical trial based on the physiology of the system of interest in order to accurately assess the effect of vitamin D in the body.


If you want both skeletal and immune system benefits from vitamin D, then it is important to get vitamin D daily – from sun, food, and/or supplements.

If you see negative results of studies the first thing to do is look at dosing – both the frequency and the amount. There needs to be enough vitamin D to make a change in status (400 IU/day probably won’t do) and it needs to be daily. The most instructive outcome will come from studies that base their results on vitamin D levels because, as you may know, there is a six-fold variability in how people respond to supplementation.

Are you taking enough vitamin D to support its daily health benefits?

Make sure you know your level of vitamin D and are taking daily steps to keep it in the target range of 40-60 ng/ml (100-150 nmol/L). Find out your levels today! Log on to the shop (click the link below) to get your tests and see for yourself if your levels can be improved.

Make sure you track your results before and after, about every 6 months!

Click Here to Access the Shop Page

How can I track my vitamin D level and intake?

To help you track your vitamin D intake along with your resulting vitamin D level, GrassrootsHealth has created an online tracking system called myData-myAnswers. You can track any of your supplemental and dietary nutrient intakes to see how they impact your levels and overall health. Check it out today!

Important Message

NEWS ALERT: States, Governments Acknowledge the Need for Vitamin D to Build the Immune System; Vitamin D*action has achieved a major milestone of ‘Moving Research into PRACTICE’!

EVERYONE needs to know about the benefits of vitamin D... We need your help to do this. Donating $25.00 today will positively affect millions of lives!

We will take this opportunity to use our extensive network to get pertinent information on vitamin D to the new US COVID Panel as well as local and state government representatives around the world.

Donate $25 today to help support this outreach effort (and, let us know if your employer could match the donations made by individuals from now until January 1, 2021!). You can also "text-to-give" by simply texting Daction to 44321.

Donations made through GiveLively are received in full by GrassrootsHealth.

What Does it Take YOU to Get Your D to 40 ng/ml (100 nmol/L)?

Did you know your health could be greatly affected by making sure you have a vitamin D level of at least 40 ng/ml (100 nmol/L)? Help us help you.

STEP 1 - Do you know what your vitamin D level is? If not, be sure to test today to find out.

STEP 2 – Determine your target level. Are you at your target level? Experts recommend a level of at least 40-60 ng/ml (100-150 nmol/L).

STEP 3 – Need to boost your level? Use the D*calculator to see how much vitamin D it may take to reach your target. Opt for the Loading Dose for a quicker boost.

STEP 4 – Optimize how your body absorbs and utilizes vitamin D with co-nutrients and these simple steps.

STEP 5 – Re-Test! This is an important step to make sure you have reached your target level, and to ensure you are not taking too much! Re-testing after 3-4 months is recommended.

STEP 6 – Adjust, Repeat…

Give your immune system the nutrients it needs to support a healthy you and protect yourself from unnecessary diseases, especially COVID-19.


The first Randomized Controlled Trial on vitamin D and COVID-19 has shown a 96% lower risk of ICU admission for those receiving vitamin D (as 25(OH)D to quickly boost vitamin D blood levels) along with the standard treatment, compared to those receiving standard treatment alone.

These results support many previous observational studies showing a relationship between vitamin D levels and intake and COVID-19 severity.

Review the Latest Nutrient Research for COVID-19

GrassrootsHealth Nutrient Research Institute has launched the new Immune Boost project with the use of our myData-myAnswers nutrient health system that nearly 15,000 people are already using for their health. Specific markers that influence immune health are suggested for testing as part of this project including:

  • Vitamin D
  • Omega-3 Index
  • Essential elements magnesium, selenium, and zinc
  • hsCRP

Our goal is to demonstrate how one can use the Nutrient Research Model established by Dr. Robert Heaney to show the effect of vitamin D serum levels of at least 40 ng/ml (100 nmol/L) on risk reduction for all ethnicities in the population. Status and intake of other nutrients will also be analyzed for any type of relationship to immune status and symptom severity. Join the project today!

Please let us know if you're interested in helping sponsor this project.

CLICK HERE for updates and new information about the project.

Through GrassrootsHealth Nutrient Research Institute, you can also test your essential elements magnesium, copper, zinc and selenium, toxins such as lead, mercury and cadmium, as well as your omega-3 levels, inflammation levels and thyroid stimulating hormone (TSH) level. Find out your levels today! Log on to the test selection page (click the link below) to get your tests and see for yourself if your levels can be improved.

Make sure you track your results before and after, about every 6 months!

Click Here to Access the Test Page

How can I track my nutrient intake and levels over time?

To help you track your supplement use and nutrient levels, GrassrootsHealth has created the Personal Health Nutrient Decision System called

For each specific supplement, you can track what days you take it, how much, and many other details.  This will help you know your true supplemental intake and what patterns of use work for you to reach and maintain optimum nutrient levels. Check it out today!