Your homocysteine is elevated, and your genes may explain why.

MTHFR encodes an enzyme that converts folate into its active form, methylenetetrahydrofolate. This active folate is essential for the methylation cycle, which recycles homocysteine back into the amino acid methionine. Every time your cells need to make new DNA, regulate gene expression, or balance neurotransmitters, they depend on methylation. It’s one of the most fundamental biochemical processes in your body.

The MTHFR C677T variant reduces enzyme efficiency by 40 to 70 percent. Roughly 40% of people with European ancestry carry at least one copy of this variant. When you inherit the T allele, your cells convert dietary folate into active folate much more slowly. That means your homocysteine accumulates because the recycling system is running at partial capacity. Standard folate supplements don’t help because your enzymes can’t process them efficiently.

You experience this as persistent fatigue despite adequate sleep, brain fog that doesn’t clear with better focus habits, and a lingering sense of not quite feeling yourself. If your homocysteine is elevated, MTHFR variants are usually a primary driver. You may also notice that B vitamin supplements don’t seem to help, or that you feel worse on certain formulations.

Factor V is a blood clotting protein that circulates in your bloodstream ready to be activated. When you have a cut, Factor V springs into action to help form a clot and stop bleeding. It’s an essential survival mechanism. Your body regulates Factor V carefully to prevent both excessive bleeding and dangerous clot formation.

The Factor V Leiden variant (R506Q), carried by roughly 5% of people with European ancestry, makes Factor V resistant to the natural anticoagulation process. When your body normally tries to shut down clotting by breaking down Factor V, this variant prevents that shutdown. Your blood clots 4 to 8 times more readily than normal, and the risk skyrockets to 80 times higher if you take oral contraceptives. If you also carry an MTHFR variant raising your homocysteine, you’re stacking two independent clotting risks.

You may experience unexplained swelling in your legs, unusually painful periods if you menstruate, a family history of blood clots or heart attacks at relatively young ages, or recurrent miscarriages if you’re pregnant. Many people carry Factor V Leiden without knowing it until a clotting event forces investigation.

Prothrombin (Factor II) is another essential blood clotting protein. Like Factor V, it must be tightly regulated. Your liver produces prothrombin in precise quantities, and when you need a clot, prothrombin is converted into active thrombin, which polymerizes fibrin and forms a plug. Too much prothrombin and you clot too easily. Too little and you bleed excessively.

The F2 G20210A variant, present in roughly 2 to 3 percent of people with European ancestry, increases prothrombin production. People with this variant produce 30 to 50 percent more prothrombin than the population average. This elevates clotting risk by 2 to 3 times and interacts multiplicatively with Factor V Leiden. If you carry both F2 and F5 variants, your cardiovascular risk rises substantially, and the combination becomes clinically significant.

You may never feel anything. Many people with F2 variants have no symptoms until a clot forms. But combined with elevated homocysteine from an MTHFR variant, or combined with F5 Leiden, the risk becomes meaningful. Family history of blood clots, strokes, or heart attacks at unusual ages often points to F2 involvement.

Plasminogen activator inhibitor-1 (PAI-1) is your body’s brake pedal on clot dissolution. After your blood clots to seal a wound, your body must eventually break the clot down and clear it. Plasmin is the enzyme that dissolves clots. PAI-1 inhibits plasmin, so it essentially applies the brakes. Your body needs both efficient clot formation and efficient clot clearance. Balance is everything.

The PAI1 4G/5G polymorphism creates two versions of the gene. People with the 4G/4G genotype, which accounts for roughly 25% of the population, produce more PAI-1 protein. Higher PAI-1 means clots persist in your bloodstream longer before being cleared. This increases the window during which a clot can lodge in an artery or travel to your lungs. The effect is compounded if you also carry MTHFR variants elevating homocysteine or F5 Leiden amplifying clot formation.

You may notice a family history of sudden cardiovascular events, persistent swelling or discoloration in your legs that doesn’t resolve quickly, or an unusual number of small bruises. Some people with high PAI-1 report feeling “off” after stressful periods, which is because stress also elevates PAI-1 temporarily.

Nitric oxide (NO) is a signaling molecule that your blood vessels produce to relax and dilate. When your body detects increased blood flow demand, endothelial cells lining your arteries release nitric oxide. NO diffuses into the smooth muscle layer of the vessel wall and tells it to relax. The artery expands, blood pressure drops locally, and more blood flows through. This is how your body maintains flexible, responsive blood vessels and prevents high blood pressure.

The NOS3 Glu298Asp variant, carried by roughly 30 to 40 percent of the population, reduces nitric oxide production by your endothelial cells. Your blood vessels remain more constricted than normal, and your body cannot dilate arteries efficiently in response to increased demand. This drives baseline blood pressure higher and accelerates atherosclerosis. If you also have elevated homocysteine, which directly damages endothelial cells, your vessel walls are under double stress.

You experience this as difficulty exercising without becoming short of breath, elevated baseline blood pressure even on a good diet and despite regular activity, or poor exercise tolerance that doesn’t improve despite consistent training. Many people with NOS3 variants notice that their blood pressure is chronically 10 to 15 points higher than peers who seem less health-conscious.

Vitamin K is a cofactor that your body absolutely requires to produce active blood clotting factors. Specifically, vitamin K activates Factors II, VII, IX, and X, all of which are essential for clot formation. Your body recycles vitamin K efficiently. After vitamin K does its job, an enzyme called vitamin K oxide reductase (encoded by VKORC1) reduces it back to active vitamin K so your body can reuse it. This recycling system is so efficient that you rarely need dietary vitamin K supplementation for clotting purposes.

VKORC1 has multiple variants that affect how efficiently it recycles vitamin K. Some variants increase recycling efficiency, while others reduce it. People with reduced-function VKORC1 variants require more dietary vitamin K to maintain normal clotting factors, and they are more sensitive to warfarin and other vitamin K antagonist medications. These individuals may find that their clotting profile is unusually variable despite consistent diet.

You may notice that your INR (International Normalized Ratio, a measure of clotting time) fluctuates significantly even when your diet and medication are consistent, or that seasonal changes in vitamin K intake seem to shift your clotting tendency. If you’re on warfarin, your dose may need adjustment more frequently than average.