Vitamin B9

Physiological Role

Folate, or vitamin B9, is a water-soluble vitamin that the body cannot synthesize. It must be obtained through diet: green leafy vegetables, legumes, liver, and citrus fruits. Once absorbed, folate is converted into 5-methyltetrahydrofolate (5-MTHF), its biologically active form. This conversion involves several successive reactions, the last of which is carried out by the enzyme MTHFR (methylenetetrahydrofolate reductase), whose activity varies with genetic profile.

5-MTHF plays a key role in the methylation cycle. It provides a methyl group to homocysteine to reconvert it into methionine, an essential amino acid. This transfer is carried out by methionine synthase and requires vitamin B12 as a cofactor. Methionine is then transformed into S-adenosylmethionine (SAM), the body's primary methyl donor. SAM is involved in gene regulation, neurotransmitter synthesis, and DNA integrity maintenance.

Serum folate is a direct measurement of circulating vitamin B9, with no intermediate calculation. It reflects intake over recent days and the state of the current diet: after about three months of steady intake, its concentration stabilizes. Red blood cell folate, which some laboratories also offer, measures a different quantity, on a scale about thirty times higher. The two results are not comparable.

Reference Ranges

Depending on the biomarker, Singular ranges are based on a synthesis of nutritional or clinical reference points and longevity research. They do not replace your laboratory's reference values or your healthcare professional's advice.

Biological Significance

Serum folate provides a direct reading of vitamin B9 status. Values within the optimal range indicate sufficient intake to support the methylation cycle and normal cell division.

Low values may reflect insufficient dietary intake, reduced intestinal absorption, or increased requirements linked to a genetic polymorphism. A sustainably low folate status is associated with elevated homocysteine, a marker of methylation cycle function that Singular measures concurrently.

Serum folate responds to recent intake: a meal, a supplement or a change in diet shifts it within hours. This is why the sample is taken in the morning, in a fasted state, and after non-prescribed supplements have been suspended. High values most often reflect a high intake, dietary or supplemental. Their interpretation depends on vitamin B12 status: an unfavourable association is observed only when vitamin B12 is low. Singular measures both markers in the same test. Regular monitoring helps distinguish a one-time variation from a lasting trend.

Serum folate is read in conjunction with vitamin B12 and homocysteine. These three markers, measured together, provide a map of the methylation cycle. Mean corpuscular volume (MCV) provides complementary information: an elevated MCV may signal increased folate or vitamin B12 requirements.

Influencing Factors

Diet. Green leafy vegetables (spinach, broccoli, asparagus), legumes, liver, and citrus fruits are the richest dietary sources of natural folates. Prolonged cooking significantly reduces folate content in food.

Meals and sampling time. Serum folate rises as soon as a meal ends and stays above its fasting value for the following twenty-four hours. A postprandial kinetics study measured almost 30% difference twelve hours after a standardized breakfast. It noted that 17% of participants would have been classified differently depending on sampling time. The Singular protocol therefore requires a morning sample, after twelve hours of fasting.

Genetics. The MTHFR C677T polymorphism occurs in homozygous form in 4 to 26% of Europeans depending on the region. Under laboratory conditions, it lowers by up to 70% the activity of the enzyme that produces the active form of folate. Serum folate in homozygous carriers is about 20 to 25% lower. Carriers have increased folate requirements.

Intestinal absorption. Dietary folates are absorbed primarily in the proximal jejunum (upper part of the small intestine). A compromised intestinal mucosa may reduce this absorption. Alcohol consumption also interferes with intestinal folate transport.

Alcohol. Regular alcohol consumption decreases intestinal folate absorption and accelerates urinary excretion. This effect is dose-dependent and represents one of the most common factors behind low folate status.

Medications. Certain medications can interfere with folate metabolism, notably methotrexate, some anticonvulsants, and oral contraceptives.

Age and increased requirements. Folate requirements increase during pregnancy and breastfeeding. With age, intestinal absorption may decrease. Older adults more frequently present low serum folate values.

Supplementation. 5-methyltetrahydrofolate (5-MTHF) is the form in which folate circulates in plasma, whichever form is ingested. A daily intake raises serum folate within a few weeks, after which its concentration stabilizes at around three months.

In the Singular Formula

Vitamin B9 is one of the markers most directly integrated into the Singular personalization engine. Serum folate serves as both a nutritional adjustment parameter and a reading point for the methylation cycle.

Below the optimal range, the formula supplies vitamin B9 as 5-MTHF (calcium L-5-methyltetrahydrofolate), at a level that follows where the result sits. Folate contributes to normal blood formation. In the first third of the optimal range, the formula keeps a maintenance dose. Beyond that, no rule adds vitamin B9 on folate status alone.

The formulation engine also accounts for homocysteine. Three conditions raise 5-MTHF to its reinforced dosage: elevated homocysteine, low vitamin B9, and a vitamin B12 that is not itself low. Folate contributes to normal homocysteine metabolism. Four conditions are met here. Vitamin B9 and vitamin B12 are optimal, homocysteine is elevated, and alkaline phosphatase is not very high. The formula then combines vitamin B9 and vitamin B12 (methylcobalamin) at their maintenance dose.

Vitamin B6 (P5P) completes this system: it is involved in the transsulfuration pathway, the other homocysteine recycling route. Its dosage is not adjusted according to serum folate.

Scientific Studies

Frequently Asked Questions