Published on October 30, 2020

How to make sure your vitamin D level remains on target as the seasons cycle

With the change in seasons approaching (it seems like winter is already here for some!) it is important to keep in mind the natural fluctuations in season and our resulting lifestyle changes, and how it all affects our health. One of the most obvious changes is the amount of sun exposure available to us on a daily basis. Whether it is due to the change in the sun’s angle and the number of hours the sun is up, the increase or decrease in clothing we wear when outside, or the weather that keeps us from going outside, changes in these daily habits will have an effect on our vitamin D levels. For those of us in the Northern Hemisphere, that will most likely mean lower vitamin D and a higher chance of being deficient.

How to Avoid Vitamin D Deficiency During the Change in Seasons

Among almost 4,000 GrassrootsHealth participants who tested their vitamin D levels and reported that they did not take vitamin D supplements, vitamin D levels peaked in the month of August and declined from there to their lowest levels during the winter months of January through March. The average vitamin D level reached at the peak was 32 ng/ml.

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Many of our participants tend to rely more on sun exposure for their source of vitamin D during the summer months and will therefore decrease supplementation during that time. However, some work indoors throughout the summer months and use sunscreen when out in the sun and must still rely on supplementation.

For those who do rely on the summer sun for vitamin D production, the change of season from summer to fall with decreased sun exposure leads to an increase in need for supplementation. This can be tricky for some, and we often receive questions about an unexpected vitamin D test result during this transition – usually a level is lower than expected, which may be due to not increasing supplementation soon enough to maintain summer levels or having summer levels that were not as high as they expected.

Since it takes 2-3 months for serum levels to fully reflect a change in intake or lifestyle, it is important to stay ahead and test regularly instead of testing after the vitamin D level has already dropped.

Once you test your vitamin D level and know where you are NOW, you can account for any upcoming changes in lifestyle over the coming months and adjust your intake to reach (or maintain) your target.

GrassrootsHealth scientists recommend a vitamin D level between 40-60 ng/ml (100-150 nmol/L) as an optimal range, however, some individuals may choose to aim slightly higher for reasons such as cancer prevention. For those who are within their target range at the first test and not expecting much change in vitamin D input — great, continue what you are doing! Others will need to take steps necessary to create change or maintain vitamin D levels resulting from changes in daily habits and lifestyle.

Use the Vitamin D*calculator

The D*calculator was developed using data from GrassrootsHealth participants, and calculates two different approximate daily dose amounts based upon your current vitamin D level, intake, and weight, and your specified target vitamin D level. The first amount calculated will get approximately 50% of individuals to their chosen target level, and the second, higher amount will get approximately 90% of individuals to their chosen target level. Whichever amount an individual chooses to use daily to help achieve and maintain their desired vitamin D level would be called their “maintenance dose.” The target vitamin D level achieved using only this dose would generally be reached within approximately 3 months of supplementation.

The new D*calculator also provides a “Loading Dose” to give users the option to choose a quicker way to achieve their desired levels. The loading dose is a higher dose split into daily increments that will increase your vitamin D levels rapidly. After the specified number of days of the loading dose, users can then take their maintenance dose to keep their levels in the target range.

Adjusting Your Vitamin D Levels

In general, when attempting to adjust your vitamin D level through a change in daily vitamin D supplementation, the time to wait between the initial test and the re-test is another important factor to consider. If testing is done too soon after the change in supplementation and/or sun exposure routine, especially if a high supplementation dose is taken over a short term, it could reflect a serum level that is still in flux (and either lower or higher than would be expected), giving a false reading of how an individual will ultimately respond to that new dose.

An example of how serum levels respond to different doses of vitamin D was published in a paper by Dr. Reinhold Vieth, wherein the average vitamin D levels of four separate groups of individuals, supplementing at different daily doses of vitamin D (400 IU, 1000 IU, 2000 IU and 10,000 IU) were tracked over the span of 2-3 months. Serum levels rose at a much higher rate during the first month of supplementation for all groups, and continued to rise at a slower pace over the following month. Levels reached a plateau by 2 months for the 400, 1000 and 2000 IU/d groups, while the 10,000 IU/d group continued to experience a slight increase. For this reason, it is recommended that individuals wait 2-3 months after adjusting their dose to re-test their vitamin D level.

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What if a lower vitamin D level is desired?

Even if your level is not in the toxic range, it may be higher than you want it to be. Vitamin D toxicity is difficult to achieve, however, it is important to know the signs and when to be concerned.

If you would like to decrease your vitamin D levels, vitamin D input must be reduced. Most often that will mean cutting back on your dose of supplemental vitamin D, and possibly your sun exposure as well. However, before doing this, consider whether a recent change in intake, such as an extra-large dose during a sickness or a recent vacation to a sunny location, may have caused a temporary high level. If your intake has been consistent, reducing your dose by 25-50% may help, followed by a re-test after about 3 to 6 months to assess your response to the lowered dose. (It is important to test again to make sure you haven’t overcorrected and caused your levels to be lower than you want). It may take at least 2-3 months for the vitamin D level to fully respond to the new intake, as illustrated in the chart below showing the response in both vitamin D3 and 25(OH)D to a single dose of 100,000 IU vitamin D3.

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What does this all mean?

Plan ahead for the change in seasons – will you need more or less vitamin D intake from supplements? Will you be expecting more or less vitamin D from sun exposure? Test your levels now, and determine if a new dose of vitamin D supplementation may need to be incorporated into your daily routine. In order to get an accurate representation of the resulting vitamin D level, it is recommended that you wait at least 2-3 months before testing again. This will allow the resulting vitamin D level enough time to adjust to the new dose and reach its plateau.

Could a nutrient deficiency be hindering your body’s ability to fight disease?

Nutrients work synergistically in order to carry out specific functions within the body. For example, we have recently discussed how different immune cells rely on a variety of nutrients, including vitamins D, C, B6, B12, zinc, and magnesium, in order to carry out their actions in an immune response. Without these necessary nutrients, immune function may be hindered.

Could a nutrient deficiency be putting a damper on your immune response? Find out by testing your vitamin D, omega-3s, magnesium and other essential elements (including selenium), as well as your inflammation levels, with the new Immune Boost home test kit offered by GrassrootsHealth. Measuring levels is the only way to know if you are supporting your immune system and whether additional changes should be made, with supplementation, dietary changes, or both.

Enroll now with the Full Immune Boost Panel (which includes tests for vitamin D, Omega-3 Index, magnesium, zinc, selenium, copper, and hsCRP), and get 10% off when you use coupon code BoostTen at checkout.

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!

How Can You Use this Information for YOUR Health?

Having and maintaining healthy vitamin D and other nutrient levels can help improve your health now and for your future. Measuring is the only way to make sure you are getting enough!

STEP 1 Order your at-home blood spot test kit to measure vitamin D and other nutrients of concern to you, such as omega-3s, magnesium, essential and toxic elements (zinc, copper, selenium, lead, cadmium, mercury); include hsCRP as a marker of inflammation or HbA1c for blood sugar health

STEP 2 Answer the online questionnaire as part of the GrassrootsHealth study

STEP 3 Using our educational materials and tools (such as our dose calculators), assess your results to determine if you are in your desired target range or if actions should be taken to get there

STEP 4 After 3-6 months of implementing your changes, re-test to see if you have achieved your target level(s)

Enroll in D*action and Build Your Custom Test Kit!