02/04/2026
I often hear people say they’re getting enough vitamin D because they eat fortified foods—milk, plant milks, or cereals.
That assumption makes sense — but the form of vitamin D added matters.
Many fortified foods contain vitamin D₂, which is consistently shown to be less effective than vitamin D₃ at raising and maintaining vitamin D levels. Research has demonstrated that consumption of vitamin D₂–fortified foods can reduce circulating 25-hydroxyvitamin D₃, the primary form your body produces from sunlight and relies on physiologically.
One practical step: read labels. If you’re relying on fortified foods, check whether they contain vitamin D₃ rather than D₂.
In clinical practice, a daily intake of approximately 1,000 IU of vitamin D₃ during the winter months is commonly used as a general maintenance range for adults. However, individual requirements vary, and measuring a 25-hydroxy vitamin D level remains the most reliable way to determine adequacy.
Who should consider testing vitamin D?
Testing is particularly useful for individuals with:
– Persistent fatigue
– Recurrent infections or slow recovery
– Chronic inflammatory conditions
– Low mood or brain fog
– Limited sun exposure
– Osteopenia or osteoporosis
– daily intake of high dosage vitamin D supplementation without testing.
In these situations, testing provides clearer guidance than guessing.
