Normal Bloodwork, Still Deficient? Your Genes May Be Why.

MTHFR encodes the methylenetetrahydrofolate reductase enzyme, which catalyzes one of the most critical steps in cellular metabolism: the conversion of dietary folate into methylfolate, the active form your cells actually use. This same enzyme is essential for converting B12 into active methylcobalamin. Your methylation cycle depends on these conversions; it powers detoxification, neurotransmitter synthesis, DNA repair, and energy production. Without efficient MTHFR activity, your entire methylation system runs at reduced capacity.

The MTHFR C677T variant, carried by approximately 40% of people of European ancestry, reduces enzyme efficiency by 40-70%. That’s not a minor slowdown. You can eat a perfect diet rich in folate and B12 and still be functionally depleted at the cellular level because your enzyme is working at 30-60% capacity. This isn’t a failure of your diet or supplementation effort; it’s a genetic bottleneck.

You experience this as persistent fatigue despite adequate sleep, brain fog that coffee doesn’t touch, low mood or anxiety that seems disconnected from your life circumstances, poor stress resilience, weak immune function, and slow recovery from illness or training. Some people report chronic pain, headaches, or chemical sensitivities. These aren’t separate problems; they’re downstream consequences of poor methylation capacity.

VDR encodes the vitamin D receptor, the protein that sits on your cell membranes and inside your mitochondria and allows vitamin D to actually do its job. Vitamin D doesn’t circulate passively; it needs to bind to VDR and enter your cells to regulate gene expression, immune function, calcium metabolism, and mitochondrial energy production. If your VDR is compromised, vitamin D accumulates in your bloodstream but can’t enter your cells effectively.

The VDR FokI variant and other common polymorphisms affect receptor sensitivity and activity. Roughly 30-50% of people carry a VDR variant that reduces cellular uptake efficiency. You can take 5,000 IU or even 10,000 IU of vitamin D daily and still have poor intracellular vitamin D status because your cells simply cannot import it efficiently. Your blood test shows adequate or even high vitamin D, but your tissues are functionally depleted.

You experience this as persistent muscle weakness or poor recovery, bone aches, autoimmune flares, poor mood (especially in winter or low-sun seasons), weak immune function, slow wound healing, or poor calcium absorption despite adequate intake. Because vitamin D regulates mitochondrial function, you may also notice unexplained fatigue or exercise intolerance.

HFE encodes a protein that regulates hepcidin, the hormone that controls iron absorption and storage. When HFE is working properly, it senses your iron status and adjusts hepcidin appropriately, preventing both iron overload and iron deficiency. Iron is essential for oxygen transport, energy production, immune function, and cognitive performance, but it must be carefully regulated because excess iron is toxic and contributes to oxidative stress and inflammation.

The HFE C282Y variant in homozygous form (two copies) causes severe iron overload, hemochromatosis, and requires iron restriction. The more common H63D variant, carried by 15-20% of people of European ancestry, is associated with mild to moderate iron dysregulation and iron-deficiency susceptibility. H63D carriers often absorb iron less efficiently and are at higher risk for iron-deficiency anemia, fatigue, and poor oxygen transport despite eating iron-rich foods. The dysregulation can swing depending on context; some carriers tend toward mild overload, others toward deficiency.

You experience this as persistent fatigue even with apparently adequate iron intake, shortness of breath with exertion, poor exercise recovery, brain fog, weak immunity, pale skin or pale mucous membranes, and sometimes heart palpitations. Women with H63D may notice heavier menstrual bleeding or more severe period fatigue.

BCMO1 encodes beta-carotene 15,15′-monooxygenase, the enzyme that converts dietary plant-based beta-carotene into retinol, the active form of vitamin A your body uses for vision, immune function, skin health, and gene expression. Vitamin A is fat-soluble and cannot be stored indefinitely, so you need continuous dietary supply. If you’re relying on plant sources (spinach, kale, carrots, sweet potato), your BCMO1 enzyme must efficiently convert them or you end up deficient despite adequate plant intake.

The BCMO1 R267S and A379V variants, carried by approximately 45% of people, reduce enzyme efficiency and the amount of beta-carotene converted to retinol. You can eat plenty of carrots and dark leafy greens and still have inadequate vitamin A status because your BCMO1 enzyme converts plant-based sources inefficiently. The deficit is compounded if you avoid animal products (eggs, liver, dairy, fish) that contain preformed vitamin A.

You experience this as poor night vision or slow adjustment to dim lighting, dry skin or frequent skin infections, weak immunity and frequent colds, poor wound healing, hormonal irregularities (vitamin A is essential for reproductive hormone metabolism), and sometimes acne or other skin inflammatory conditions. Some people report thinning hair or dry mucous membranes.

FUT2 encodes a fucosyltransferase that determines the composition of your gut microbiome by influencing which bacteria preferentially colonize your intestines. Your microbiome is not just passengers; they synthesize B vitamins, regulate intestinal barrier integrity (leaky gut vs. tight junctions), produce short-chain fatty acids, and control the pH and environment that determines how efficiently you absorb minerals and other nutrients. A dysbiotic microbiome reduces nutrient bioavailability dramatically, even if you eat perfectly.

FUT2 variants, common across populations, are associated with significantly reduced Bifidobacterium and other beneficial bacteria and increased pathogenic species. FUT2 non-secretor status (certain variants) correlates with reduced B12 and vitamin D absorption, impaired iron bioavailability, and poorer overall micronutrient status despite adequate dietary intake. Your microbiome composition is essentially determined by your FUT2 genotype, which means you cannot supplement your way out of this without addressing the bacterial ecology.

You experience this as chronic bloating or digestive distress even with a clean diet, persistent nutrient deficiencies despite supplementation, food sensitivities or reactions that seem inconsistent, frequent infections, or slow recovery from illness. Some people notice that they absorb nutrients well when taking probiotics or eating fermented foods, and poorly when they don’t.

COMT encodes catechol-O-methyltransferase, an enzyme that metabolizes dopamine, norepinephrine, and epinephrine (your stress neurochemicals). COMT also requires magnesium, B vitamins, and other micronutrients as cofactors to function. People with COMT variants have altered catecholamine metabolism, which changes their micronutrient needs. Fast COMT variants clear catecholamines rapidly (you’re less sensitive to stress but may feel unmotivated or low-dopamine). Slow COMT variants clear them slowly (you’re highly sensitive to stress, caffeine, and stimulants and may accumulate too much dopamine under stress).

The COMT Val158Met variant, extremely common, creates fast and slow metabolizer categories. Slow COMT carriers require significantly higher magnesium and B vitamins to support their elevated enzyme activity and to counterbalance their tendency toward catecholamine accumulation under stress. Roughly 40% of people carry at least one slow-metabolizer allele. Taking standard supplementation while having slow COMT and high stress can leave you deficient in these critical micronutrients because your body is burning through them faster.

You experience this as difficulty handling stress or stimulation, poor stress resilience, anxiety or irritability that feels out of proportion to events, poor sleep (especially when stressed), tension headaches, and sometimes high or irregular blood pressure under stress. Some slow-COMT people are sensitive to caffeine, supplements, or medications. The micronutrient depletion manifests as additional fatigue, muscle tension, or mood instability.