Vitamin B6 (Pyridoxine) for Kidney Stones

Vitamin B6 has not been shown to prevent common kidney stones. Across three US cohorts of 193,551 men and women followed for 3.3 million person-years, people getting 40 mg a day or more had the same risk of a first stone as those getting under 3 mg (pooled HR 1.03, 95% CI 0.92 to 1.15) (Ferraro 2018). An earlier analysis in 85,557 women had found a lower risk at that intake (RR 0.66, 95% CI 0.44 to 0.98) (Curhan 1999), but the 2018 analysis, which included two cohorts of women, found no link in either.

B6 matters for stones in one setting: primary hyperoxaluria type 1 (PH1), a rare inherited disease in which the liver overproduces oxalate, leading to recurrent stones and eventually kidney failure (Groothoff 2023). Pyridoxine supplies the cofactor of the faulty liver enzyme (Fargue 2013), and in a prospective trial of 12 people with PH1, rising doses up to 20 mg/kg a day cut urine oxalate by 30% or more in half of them (Hoyer-Kuhn 2014). European expert guidelines recommend starting pyridoxine in everyone with suspected or proven PH1 (Groothoff 2023).

Pyridoxine is converted to pyridoxal phosphate, the essential cofactor of alanine:glyoxylate aminotransferase (AGT), a liver enzyme. A deficiency of AGT causes PH1 (Fargue 2013), and restoring its activity, as a liver transplant does, lets the liver handle glyoxylate again and stops the excess oxalate (Gupta 2022). In laboratory cells carrying the most common responsive mutation, Gly170Arg, pyridoxine raised the amount of AGT, its activity and its delivery to peroxisomes, the cell compartment where it works, so it acts both as a cofactor and as a chemical chaperone (Fargue 2013).

That is why the response depends on genotype. In 23 people with PH1, urine oxalate normalised on B6 in those with two copies of the c.508G>A (Gly170Arg) change, fell partly in those with one copy, and did not change significantly in those with none (Monico 2005). Partial effects were also seen in cells with the Phe152Ile and Ile244Thr mutations, but not with Gly41Arg (Fargue 2013).

Most kidney stones aren't caused by a faulty enzyme, and the B6 story doesn't carry over well. Male stone formers had slightly lower blood pyridoxal phosphate than healthy men (59.6 and 64.9 versus 86.0 nmol/L), whether or not their urine oxalate was high, yet B6 levels didn't correlate with urine oxalate, before or after a week of 300 mg a day, and none were B6 deficient (Kaelin 2004). Another study likewise found that high oxalate excretion didn't necessarily go with low B6 status (Tolomelli 1991).

Lower urine oxalate is also a stand-in for the outcome that matters. Outside PH1, no controlled study has shown that a fall in oxalate on B6 means fewer stones.

For common calcium oxalate stones there is no proven dose. Studies in people with idiopathic hyperoxaluria (high urine oxalate without a genetic cause) used anything from 10 mg a day (Murthy 1982) through 25 mg with 400 mg magnesium oxide (Gupta 2021) and 50-200 mg (Ortiz-Alvarado 2011) to 250-500 mg a day (Mitwalli 1988). The cohorts' top group took 40 mg a day or more (Ferraro 2018). For comparison, most adults need only 1.3-1.7 mg a day, or 1.9-2.0 mg in pregnancy and breastfeeding (NIH ODS). Almost all of these doses sit above the European upper limit of 12 mg a day (EFSA 2023), and the highest exceed the US limit of 100 mg a day (NIH ODS).

In PH1, the EAU guideline lists pyridoxine at 5 mg/kg a day to start, up to 20 mg/kg a day (EAU guideline). The European PH consensus suggests a maximum of 5 mg/kg, because long-term high doses are potentially neurotoxic, and higher doses only in selected patients under close monitoring (Groothoff 2023); one study found 5 mg/kg a day appeared sufficient (Monico 2005). For a 70 kg adult, 5 mg/kg is 350 mg a day. Upper limits don't apply to people taking B6 as medical treatment, who should be under a physician's care (NIH ODS).

In 45,251 US men aged 40-75 followed for 6 years (751 stones), B6 intake of 40 mg a day or more versus under 3 mg had an age-adjusted relative risk of 0.91 (95% CI 0.64 to 1.31) (Curhan 1996). In 85,557 women followed for 14 years (1,078 stones), the same comparison gave a relative risk of 0.66 (95% CI 0.44 to 0.98), and the authors suggested large doses might lower risk in women (Curhan 1999).

A 2018 analysis covered three cohorts: 42,919 men, 60,003 older women and 90,629 younger women, with 6,576 confirmed stones over 3,316,846 person-years. The top intake group had no lower risk in any of them (HR 1.05 in men, 0.95 and 1.06 in women; pooled HR 1.03, 95% CI 0.92 to 1.15), and the authors concluded B6 intake isn't associated with stone risk (Ferraro 2018). A US cross-sectional survey linked higher B6 intake with fewer people having had stones (OR 0.76, 95% CI 0.62 to 0.93), but a snapshot can't show which came first (Zeng 2024).

The only randomised trial enrolled 164 calcium oxalate stone formers with newly diagnosed idiopathic hyperoxaluria and assigned them to a low-oxalate diet, 25 mg B6 plus 400 mg magnesium oxide, or both. After 12 weeks, median urine oxalate fell 31.1% on diet, 16.0% on the supplement and 23.9% on both (p = 0.007), and 91.4%, 67.6% and 86.7% saw any fall. Only 99 people finished, there was no placebo arm, and stones weren't counted (Gupta 2021).

Older studies were small and uncontrolled. In 12 recurrent stone formers, 10 mg a day lowered urine oxalate significantly by day 90 (Murthy 1982); in another 12, oxalate fell from 480 to 336 µmol a day within 6 weeks (Balcke 1983); and in 12 more, 250-500 mg a day lowered oxalate for up to 18 months, with 8 showing no active stone disease, 3 slight growth of old stones and 1 a new stone (Mitwalli 1988). In a retrospective series of 95 patients given dietitian counselling plus 50-200 mg of B6, urine oxalate fell from 58.3 to 40.6 mg a day and 39% reached the normal range, but diet and B6 can't be separated (Ortiz-Alvarado 2011).

B6 also turns up in combination products. In a 3-year study, a syrup of potassium citrate, magnesium citrate and 20 mg pyridoxine per 5 mL, taken every 8 hours, cut recurrence from 3.23 to 0.35 stones per patient a year. The comparison groups were people who stopped the drug or had milder disease rather than a randomised control, and the authors credited the citrate (Reddy 2014); see potassium for kidney stones and magnesium for kidney stones.

In the first prospective trial of B6 in PH1, 12 patients with normal kidney function took 5 mg/kg a day, rising every 6 weeks to 20 mg/kg by week 24. Urine oxalate fell on average 25.5%, from 2.09 to 1.52 mmol/1.73 m² a day (P = 0.01), and 6 of 12 reached the 30% response threshold: all 3 with two copies of Gly170Arg, 1 of 5 compound heterozygotes and 2 of 4 with neither common mutation. No one reached complete biochemical remission (Hoyer-Kuhn 2014).

About a third of PH1 patients respond to pyridoxine (Fargue 2013), and response is defined as a fall in urine oxalate of more than 30% (Gupta 2022). An RNA interference drug approved in 2020 now adds another option (Gupta 2022): in a phase 3 trial of 39 patients aged 6 or older, lumasiran cut urine oxalate by 65.4% over 6 months, 53.5 percentage points more than placebo, and 84% reached near-normal levels versus none on placebo (Garrelfs 2021).

B6 from food hasn't been reported to cause harm, but supplements can. Taking 1-6 g a day for 12-40 months can cause severe, progressive sensory neuropathy with loss of coordination, and several reports describe neuropathy at doses below 500 mg a day (NIH ODS). Healthy volunteers given 1 or 3 g a day developed sensory symptoms, sooner at the higher dose, and symptoms kept progressing for 2-3 weeks after stopping (Berger 1992). The US upper limit is 100 mg a day for adults (NIH ODS). In 2023 the European Food Safety Authority set it at 12 mg a day for adults, including in pregnancy and breastfeeding, starting from 50 mg a day, an intake it identified from a case-control study of neuropathy supported by case reports (EFSA 2023). Limits are lower for children: 30-80 mg a day in the US depending on age (NIH ODS) and 2.2-10.7 mg a day in Europe (EFSA 2023). See peripheral neuropathy.

The stone studies reported few problems: no significant adverse events in the 12-week trial (Gupta 2021), no significant complications at 250-500 mg a day (Mitwalli 1988), and no peripheral neuropathy at up to 200 mg a day over a mean of 18 months (Ortiz-Alvarado 2011). These were small or short studies, so they can't rule out nerve damage. People with chronic kidney disease or on dialysis often have low B6 levels (NIH ODS), so any B6 dose should be agreed with their kidney specialist.

A few interactions matter. Pyridoxine at 200 mg a day for 12-120 days can lower blood levels of phenytoin and phenobarbital, and antiepileptics including valproic acid, carbamazepine and phenytoin speed up B6 breakdown, lowering B6 levels (NIH ODS). The tuberculosis antibiotic cycloserine increases urinary loss of B6, and supplements can help prevent the resulting side effects (NIH ODS). People taking theophylline for lung disease often have low B6 levels, which could contribute to its nervous system side effects (NIH ODS).

B6 also comes in B-complex and multivitamin products, so add up every source before judging your dose. And B6 doesn't replace the measures with better evidence for stones, such as more fluid and the alkaline citrates the EAU guideline lists for some urine profiles (EAU guideline).