We’ve all done it—grabbed a multivitamin, popped it in the morning, and hoped we were covered. But just because we take a vitamin doesn’t mean our bodies absorb or use it as we expect.
Are our vitamins actually working for us?
The Vitamin Myth
It’s easy to think of vitamins like fuel—fill the tank, and the body runs smoothly. But the reality is more complicated. Vitamin absorption is more like a recipe, where age, genetics, and gut health determine how well nutrients are used.
“Tell me what you digest and absorb, and I will tell you what you are,” the researchers wrote. In other words, two people can take the same supplement, but their bodies may process it differently. So, if you rely on a one-size-fits-all approach to vitamins, you might not get what you think.
The Vitamin B12 Example
The UCSF study found that even with “normal” B12 levels, some people weren’t reaping the benefits. Some had too little active B12 (holo-transcobalamin), the form the body uses, while others had excess inactive B12 (holo-haptocorrin), which circulates in the blood but isn’t available to cells.
Brain scans showed significant consequences. Those with low active B12 had slower cognitive processing and more white matter lesions, changes associated with neurodegeneration and aging. Meanwhile, high levels of inactive B12 were associated with increased Tau proteins, a marker linked to Alzheimer’s.
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What Else We Might Be Getting Wrong
- Vitamin D: Research in Clinical Biochemistry Reviews found that genetics, body mass index, and ethnicity affect how well the body absorbs and uses vitamin D. Some people need higher doses to maintain healthy levels, while others struggle to activate the vitamin.
- Iron: Unneeded iron supplements can increase oxidative stress, a risk factor for diabetes and certain cancers. Unlike water-soluble vitamins, excess iron isn’t easily flushed out, leading to toxic buildup.
- Magnesium & Zinc: The type of supplement matters. Magnesium citrate is better absorbed than magnesium oxide. Similarly, zinc picolinate is more bioavailable than zinc gluconate, meaning your body can use it more efficiently.
How Do You Know If Your Vitamins Are Working?
So, how can you tell if your body is using the vitamins you take? Pay attention to how you feel. Persistent fatigue, brain fog, brittle nails, or muscle weakness could signal a deficiency.
Testing can help, but context matters. A blood test might show your levels are “normal,” but that doesn’t always mean optimal. Many vitamins are stored in the tissues, which is not reflected in the blood. Levels may fluctuate based on recent intake.
If you’re experiencing symptoms of deficiency, ask your doctor about functional tests that assess how well your body is actually using key nutrients.
