You take vitamin D every day, your blood test still comes back low, and you're told to take more. It's a common loop, and for some people the reason sits in their DNA rather than their routine.
Your body's vitamin D supply chain
Vitamin D from sunlight or a supplement isn't usable straight away. Your liver first converts it into the form your blood test measures, using an enzyme made by the CYP2R1 gene. A carrier protein made by the GC gene then moves it around your bloodstream. Another gene, DHCR7, affects how much of the raw material your skin has to make vitamin D from sunlight, and CYP24A1 controls how quickly your body breaks it down. A small change in any one of those steps can change the number on your test.
What the biggest study found
In 2010, researchers analysed the DNA and vitamin D levels of about 30,000 people of European descent. Those same four genes stood out: GC, DHCR7, CYP2R1 and CYP24A1. People who carried the most risk variants across them had 2 to 2.5 times the odds of being vitamin D insufficient compared with people who carried the fewest.
Source: Wang et al., The Lancet, 2010.
What to do if you're always low
Start with a blood test for 25-hydroxyvitamin D, the standard measure, so you know your real starting point instead of guessing. Take vitamin D3 rather than D2, and take it with your largest meal, because it's fat-soluble and absorbs better alongside food that contains fat. Then retest after about three months to see whether your dose actually moved the number. If you carry several risk variants, expect a standard dose to do less for you than it does for most people, and let your blood result, not the label, decide what comes next.
More isn't automatically better. Vitamin D is stored in your body, so very high doses taken for a long time can build up. Your dose should be set by your blood levels and your doctor.
Find out your type
Myoform's test reads your whole genome, including GC, DHCR7, CYP2R1 and CYP24A1, and combines it with your blood biomarkers to set the vitamin D in your blend. Get your genetic test.
The Decode is for education only and isn't medical advice.