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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.

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!