Published on January 5, 2022

Did your vitamin D result come back lower than expected with no change in your supplement amount? Here are some possible reasons why and questions to ask if it happens to you.

Key Points

  • There are several reasons a vitamin D test result may be lower than expected when maintaining the same usual supplemental dose of vitamin D
  • First, be sure the same testing method was used for any vitamin D results being compared
  • Consider each factor below to see if it could have contributed to a lowered vitamin D test result

On occasion we have participants who receive a lower than expected vitamin D result, especially when compared to a previous level. If you have been consistently taking the same supplemental dose of vitamin D and experience an unexpected drop in your vitamin D result, it’s possible that a change in diet, behavior, health, or the environment over the prior few months could have reduced your levels. In this blog we explore possible causes of a lower than expected vitamin D result or an unexpected drop from a previous result.

Testing Method Used – Are you comparing results from the same testing method?

Sometimes, participants compare a GrassrootsHealth vitamin D test result to one obtained using another laboratory testing method. This has been known to create confusion for participants when testing their vitamin D levels through GrassrootsHealth and another lab (such as through their doctor) around the same time, or when comparing previous vitamin D results from different providers to a GrassrootsHealth result.

The most common type of laboratory testing method used to measure vitamin D by doctors and hospitals is called an immunoassay. Unfortunately, this type of test can be affected by excess biotin in the blood (either from a biotin supplement or from a B-complex), as many of these tests use biotin as part of its testing method. When testing vitamin D levels using these immunoassays, biotin interference can cause a falsely high result.

It is important to note that none of the testing methods use for the tests offered by GrassrootsHealth are affected by biotin, which means a GrassrootsHealth vitamin D result may be lower than one from a doctor’s office. For vitamin D specifically, the testing method used by GrassrootsHealth is called LC-MS/MS (liquid chromatography – mass spectrometry), which is considered the gold standard for 25(OH)D testing.

Time of Blood Sampling – What time of day was the vitamin D blood drawn for the test?

For individuals tracking their vitamin D levels, it would be best to collect your blood sample at the same time of day to have a consistent measurement over time, as vitamin D levels fluctuate throughout the day.  A study by GrassrootsHelath found that mid-day vitamin D levels were approximately 20% higher than morning levels and approximately 13% higher than evening levels. Taking a vitamin D supplement before or after testing did not make a difference.  Previous studies have also noted a variation in vitamin D levels based on time of day.

Supplement Intake & Routine – What may be different besides average daily intake?

If the amount of vitamin D taken on a daily basis has not changed, there are still other things to consider with an unexpected drop in vitamin D level in relation to vitamin D supplementation. Changing the product or brand of your vitamin D supplement can affect how much vitamin D is available and absorbed. Check the label of your supplement to make sure the serving size or amount of vitamin D per serving hasn’t changed (it’s known to happen, even for the same product!). Taking the supplement with or without a meal can also have an effect, as some studies show that more vitamin D is absorbed when it is taken with a fatty meal. Also, try to remember if an extra large dose of vitamin D was taken before the previous test, which could have caused a higher vitamin D result for the usual average dose taken.

Vitamin D Co-Factors & Competitors – Could you be getting more or less of other nutrients that affect vitamin D levels?

The intake of other nutrients has been shown to impact vitamin D levels. For example, a lack of key vitamin D co-factors such as magnesium, vitamin K, boron, and zinc can reduce vitamin D adsorption and production. A change in diet or other supplements taken may therefore lead to a decrease in these important co-nutrients, possibly resulting in a lower vitamin D result.

On the other hand, a high intake of certain vitamins that compete with vitamin D, such as Vitamin A in the form of retinol or retinyl palmitate (not beta-carotene), can cause a reduction in vitamin D levels. This form of vitamin A is found in food from animal sources (especially liver) and some supplements.

Dietary Intake of Vitamin D – Are you eating fewer foods that contain vitamin D?

Certain foods that have naturally occurring vitamin D (e.g. fish, meat, and eggs) or are fortified with vitamin D (e.g. milk and other dairy products, some orange juice and cereals) can impact vitamin D levels. Reduced consumption of these foods many lower vitamin D levels. Additionally, some foods contain vitamin D2 (not D3) such as mushrooms and some fortified foods (e.g. rice milk and soy milk) and while our body can use this form, it isn’t as effective as vitamin D3. Further, the amount of vitamin D available in food is rather small compared to what most people need to achieve a blood level of at least 40 ng/ml (e.g. salmon has ~450 IU/serving and fortified milk has ~120 IU/cup).

Sunshine & UVB Exposure – Are you getting less UVB?

A decrease in UVB exposure could contribute to a lower vitamin D level. Perhaps a vacation to a sunny location was taken prior to the previous vitamin D test, but not prior to the most recent test?

When relying more heavily on sun exposure and/or indoor tanning for vitamin D, not exposing enough skin, high sunscreen use, or lack of mid-day (10 am – 2 pm) exposure will limit vitamin D production. The season and other environmental factors, such as smog, cloud cover, or residing in a higher latitude, will also influence exposure to UVB radiation. Additionally, the amount of melanin in the skin influences vitamin D production. Someone with more melanin (darker skin) might need 30 minutes in the sun to achieve the same production of vitamin D that someone with less melanin (lighter skin) will achieve in 10 minutes.

Recent Medical Conditions – Has there been a change in health?

A recent illness or injury, or even a highly stressful event, may result in a lower vitamin D level. Digestive conditions such as irritable bowel disease, Crohn’s disease, leaky gut, or celiac disease can limit the absorption of vitamin D in the gut. Those with diseases of the liver (e.g. fatty liver) or pancreas, who have had their gallbladder removed, or who have had bariatric surgery bypassing the small intestine are more likely to have trouble absorbing or metabolizing vitamin D. For these individuals, an increased dosage or other vitamin D metabolites may be needed (please consult with your physician if this is the case).

Medications – Are you taking any new or different medications?

Some medications including statins, prednisone and weight-loss drugs, can block vitamin D absorption and/or metabolism, increasing the risk of low vitamin D levels and vitamin D deficiency.  Review this full list of medications that may affect a vitamin D level to see if a medication you have recently started taking may be contributing to a lower level.

Demographic Characteristics – What else has changed?

With increased age comes a reduced ability to absorb vitamin D though the skin and a reduction in the kidney’s ability to convert vitamin D to its active form. Smokers, heavy drinkers, and those with a high BMI also tend to have lower levels. Have any of these changed for you? Could some other recent change in lifestyle or environment be impacting your vitamin D level?

Vitamin D is an Easily Modifiable Factor to Help Improve Disease Outcomes – Check Your Level Today

Having and maintaining healthy vitamin D levels and other nutrient levels can help improve your health now and for your future. Choose which to measure, such as your vitamin D, omega-3s, and essential minerals including magnesium and zinc, by creating your custom home test kit today. Take steps to improve the status of each of these measurements to benefit your overall health. You can also track your own intakes, symptoms and results to see what works best for YOU.

Enroll and test your levels today, learn what steps to take to improve your status of vitamin D (see below) and other nutrients and blood markers, and take action! By enrolling in the GrassrootsHealth projects, you are not only contributing valuable information to everyone, you are also gaining knowledge about how you could improve your own health through measuring and tracking your nutrient status, and educating yourself on how to improve it.

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!