Vitamin D deficiency occurs when your body lacks adequate levels of vitamin D, an essential nutrient for bone health, immune function, and calcium absorption. It is caused by insufficient sun exposure, inadequate dietary intake, malabsorption disorders, or kidney and liver diseases that prevent vitamin D activation. The Vitamin D, 1,25-Dihydroxy, LC/MS/MS test is the most important test for diagnosis because it measures the active form of vitamin D in your blood.
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Vitamin D deficiency is caused by insufficient sun exposure, inadequate dietary intake, malabsorption disorders, or impaired kidney and liver function. Your body produces vitamin D when your skin is exposed to sunlight, specifically UVB rays, but factors like living in northern latitudes, wearing sunscreen consistently, having darker skin, or spending most time indoors can limit production. Additionally, conditions like Crohn disease, celiac disease, and kidney or liver disease can prevent your body from absorbing or converting vitamin D into its active form, leading to deficiency even with adequate sun exposure.
The Vitamin D, 1,25-Dihydroxy, LC/MS/MS test is the most important test for vitamin D deficiency because it measures the active form of vitamin D in your blood, including both vitamin D2 and D3 metabolites. This test provides the most accurate assessment of your vitamin D status and can detect deficiency that may lead to bone diseases like rickets in children and osteomalacia in adults. For a more comprehensive evaluation, especially if you have other health concerns, the Post COVID-19 Expanded Panel includes vitamin D testing along with other important markers that can identify deficiency manifesting as bone pain and muscle weakness.
You should get tested if you experience bone pain, muscle weakness, frequent infections, fatigue, or mood changes like depression. Testing is especially important if you have limited sun exposure, darker skin, are over age 65, have obesity, kidney or liver disease, or take medications that interfere with vitamin D absorption. You should also consider testing if you have conditions like osteoporosis, inflammatory bowel disease, or if you are pregnant or breastfeeding, as these situations increase your risk of deficiency and require optimal vitamin D levels for health.
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What this means
Your testosterone levels are slightly below the optimal range. While this is not necessarily cause for concern, it may contribute to occasional fatigue, reduced motivation, or lower muscle mass over time.
Recommended actions
Increase resistance or strength training
Prioritize 7–8 hours of quality sleep per night, try to reduce stress
Include more zinc- and magnesium-rich foods (like shellfish, beef, pumpkin seeds, spinach)
Consider retesting in 3–6 months
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