Vitamin D deficiency is strikingly common among people with epilepsy, affecting roughly half of those newly diagnosed and a similar proportion of those on long-term anti-seizure medication. The connection runs in both directions: epilepsy itself and the medications used to treat it can drive vitamin D levels down, and emerging evidence suggests that low vitamin D may in turn worsen seizure control. Whether supplementation can meaningfully reduce seizures remains an open and genuinely contested question, but the case for monitoring and correcting deficiency in people with epilepsy is already strong on other grounds, particularly bone health.
How Common Is Vitamin D Deficiency in Epilepsy?
A 2024 systematic review and meta-analysis pooling data from multiple studies found that about 50% of people were vitamin D deficient at the time of a new epilepsy diagnosis, and roughly 48% of those already on anti-seizure medication were deficient as well.1PubMed Central. Vitamin D content and prevalence of vitamin D deficiency in patients with epilepsy: a systematic review and meta-analysis Those numbers are high, though some context matters: vitamin D deficiency is widespread in the general population too, especially in regions with limited sun exposure. One study in young epilepsy patients and matched controls found that more than 90% of both groups were deficient, suggesting that background rates in the study population were already very high.2PubMed. Bone health and vitamin D status in young epilepsy patients on valproate monotherapy So the question is not just whether epilepsy patients have low vitamin D, but whether their levels are lower than expected, and what that means for their health.
A retrospective study from a large epilepsy center in Saudi Arabia reported that patients with higher vitamin D levels had about 40% fewer seizures and better overall seizure control compared to those with low levels.3PubMed Central. Association between serum vitamin D levels and age in patients with epilepsy: a retrospective study from an epilepsy center in Saudi Arabia That kind of association is suggestive but does not prove causation. People with better-controlled epilepsy may simply be healthier overall, more active, and spending more time outdoors. Disentangling cause from correlation has been a persistent challenge in this field.
How Anti-Seizure Medications Deplete Vitamin D
The most well-understood part of the vitamin D-epilepsy connection involves the medications themselves. Several older anti-seizure drugs, including phenytoin, carbamazepine, phenobarbital, and primidone, are known as enzyme-inducing medications. They ramp up the activity of liver enzymes in the cytochrome P450 system, which accelerates the breakdown of vitamin D into inactive forms.4Iranian Journal of Child Neurology. How Antiepileptics May Change the Serum Level of Vitamin D, Calcium, and Phosphorus in Children with Epilepsy Your body has a certain supply of vitamin D circulating in the blood, and these drugs essentially speed up its clearance, leaving less of the active form available.
Valproate works through a different mechanism. It is not a strong enzyme inducer, yet studies have found it alters bone turnover markers in adults with epilepsy.5PubMed. Effects of valproate, lamotrigine, and levetiracetam monotherapy on bone health in newly diagnosed adult patients with epilepsy The same study found that lamotrigine and levetiracetam, two newer-generation medications, did not show harmful effects on bone health. That said, a randomized trial comparing levetiracetam to older drugs found that both groups experienced bone loss at fracture-relevant sites over one year, with no significant difference between them.6PubMed. Monotherapy with Levetiracetam Versus Older AEDs: A Randomized Comparative Trial of Effects on Bone Health The picture is not as clean as “old drugs bad, new drugs safe.” Physical inactivity, seizure-related falls, and the underlying neurological condition itself all contribute to bone and vitamin D problems in ways that are hard to separate from the medication effects.
What Vitamin D Does in the Brain
The idea that vitamin D might influence seizure activity directly, rather than just being depleted as a bystander, has been building over the past two decades. Researchers have identified functional vitamin D receptors in the hippocampus, a brain region central to many forms of epilepsy. These receptors sit on neurons and glial cells in areas like CA1, CA3, and the dentate gyrus, and they can bind to DNA, meaning they are capable of influencing gene expression in the brain.7PubMed. Evidence of functional vitamin D receptors in rat hippocampus
The active form of vitamin D appears to modulate calcium and other ion channels in the brain’s cortex, which are fundamental to how neurons fire. Research in young rats found that vitamin D influenced calcium uptake through voltage-dependent calcium channels and affected potassium and chloride channel activity as well.8PubMed Central. 1α,25-dihydroxyvitamin D(3) mechanism of action: modulation of L-type calcium channels leading to calcium uptake and intermediate filament phosphorylation in cerebral cortex of young rats Ion channel dysfunction is at the heart of many seizure disorders, so the finding that vitamin D modulates these channels offers a plausible biological pathway for anticonvulsant effects.
Animal studies have fleshed this out further. In mice given a chemical that induces seizures, vitamin D treatment led to longer time before seizures began, shorter seizure duration, and lower mortality compared to untreated animals.9PubMed. Anticonvulsant effects of 1,25-dihydroxyvitamin D in chemically induced seizures in mice In a rat model of chronic epilepsy, vitamin D reduced seizure activity and oxidative stress in the brain, and these effects were stronger when combined with lamotrigine.10PubMed. Vitamin D enhances antiepileptic and cognitive effects of lamotrigine in pentylenetetrazole-kindled rats There is also evidence of neuroprotection: in rats with severe seizure-induced brain injury, vitamin D significantly reduced the activation of microglia, the brain’s immune cells, and protected hippocampal neurons from damage.11American Epilepsy Society. VITAMIN D IS NEUROPROTECTIVE AGAINST NEURONAL INJURY FOLLOWING LITHIUM-PILOCARPINE INDUCED STATUS EPILEPTICUS BY INHIBITING ACTIVATION OF MICROGLIA Another rat study found that vitamin D prevented behavioral impairments and brain oxidative stress following seizures, with improved outcomes for the neurotransmitters GABA and glutamate.12PubMed. Neuroprotective effects of vitamin D alone or in combination with lamotrigine against lithium-pilocarpine model of status epilepticus in rats
These animal findings are genuinely encouraging, but translating results from chemically induced seizures in rodents to human epilepsy is a big leap. Many compounds that look anticonvulsant in animal models fail to show benefits in clinical trials. The biology is plausible. The human evidence, as we’ll see, is more complicated.
Does Supplementation Actually Reduce Seizures?
This is the question people care about most, and the honest answer is that the evidence is frustratingly mixed. A small pilot study in 2012 found that correcting vitamin D deficiency in people with epilepsy led to a 40% median reduction in seizures over 90 days.13PubMed. Correction of vitamin D deficiency improves seizure control in epilepsy: a pilot study That finding attracted attention, but the study had no control group and was small.
More rigorous trials have followed. A randomized clinical trial published in Epilepsia in 2024 gave high-dose vitamin D or placebo to people with drug-resistant epilepsy and found no significant difference in seizure frequency after a three-month blinded period. However, when all participants received vitamin D in an open-label extension, seizure frequency dropped by about 30% over twelve months, and bilateral tonic-clonic seizures (the most severe type) dropped by about 52%. Quality of life and fatigue also improved. The authors noted that seizure reduction correlated with maintaining vitamin D levels above 30 ng/mL for more than six months, suggesting that any effect may require sustained correction rather than a short course.14PubMed. Vitamin D deficiency and effect of treatment on seizure frequency and quality of life parameters in patients with drug-resistant epilepsy: a randomized clinical trial
A 2025 double-blind, placebo-controlled trial from India was less encouraging. After six months, the vitamin D group and the placebo group showed no significant difference in monthly seizure frequency, and the 50% responder rates were nearly identical (about 37% versus 35%).15PubMed. Role of vitamin D supplementation and vitamin D receptor in drug-resistant epilepsy: A double-blind placebo-controlled trial conducted in India A 2025 systematic review and meta-analysis also found no significant difference in baseline vitamin D levels between people with drug-resistant epilepsy and those whose seizures responded to medication, which complicates the idea that low vitamin D drives treatment resistance.16PubMed. Impact of vitamin D supplementation and status on seizure frequency and quality of life in drug-resistant epilepsy: A systematic review and meta-analysis
The pattern across all these studies is that short-term blinded comparisons generally show no clear benefit from supplementation for seizure control, while longer-term and open-label results look more promising. Open-label results are always harder to trust because both patients and doctors know they are receiving the active treatment, which introduces bias. That does not mean the longer-term findings are wrong, but it means they need confirmation from longer, blinded trials before anyone can say vitamin D is an anticonvulsant therapy in humans.
Bone Health Is the More Established Concern
While the seizure-reduction evidence remains contested, the bone health argument for vitamin D monitoring in epilepsy is on much firmer ground. People with epilepsy on anti-seizure medication face a two- to six-fold increase in fracture risk compared to the general population, and somewhere between 11% and 31% of patients develop osteoporosis.17PubMed. Impaired bone health as a co-morbidity of epilepsy The enzyme-inducing medications discussed earlier are a major driver, but the problem extends beyond a single drug class.18PubMed Central. Antiepileptics and bone health
This fracture risk compounds quietly. Many people with epilepsy take medication for decades, beginning in childhood or adolescence when bones are still building peak density. Falls during seizures add mechanical insult on top of weakened bone. For people with intellectual or physical disabilities and limited mobility, the combination is especially dangerous. A narrative review in Epilepsia recommended that regular vitamin D testing in all people with epilepsy is a cost-effective, practical step, with bone density scans added for higher-risk patients.19PubMed. Vitamin D prophylaxis in persons with epilepsy? Even without proof that vitamin D supplements improve seizure control, protecting bone density in a population at high fracture risk is reason enough to check and correct deficiency.
Children and Epilepsy Medication
Pediatric epilepsy raises distinct vitamin D concerns because children are still growing and building bone. A randomized controlled trial found that after six months of maintenance vitamin D, a higher dose (1,000 IU daily) kept more children in the adequate range than the standard 400 IU dose. Among children on a single anti-seizure medication, the proportion who were seizure-free rose from 69% at baseline to about 84% after vitamin D deficiency was treated.20PubMed Central. Vitamin D Supplementation for Children with Epilepsy on Antiseizure Medications: A Randomized Controlled Trial That is a notable improvement, though other factors could contribute in a growing child whose epilepsy is also maturing.
For children specifically on valproate, a separate randomized trial showed that daily vitamin D supplementation reduced the decline in vitamin D levels and offset the negative impact on other bone mineral markers that valproate can cause.21PubMed. Effect of Daily Vitamin D Supplementation on Serum Vitamin D Levels in Children with Epilepsy Receiving Sodium Valproate Monotherapy: A Randomized, Controlled Trial Current expert opinion suggests children with epilepsy should at minimum receive the recommended daily intake of vitamin D for their age, with additional monitoring and higher-dose supplementation if they are at increased risk of deficiency, such as those on polytherapy, enzyme-inducing drugs, or with limited outdoor activity.19PubMed. Vitamin D prophylaxis in persons with epilepsy?
The Ketogenic Diet Adds Another Layer
The ketogenic diet, a high-fat, low-carbohydrate regimen used to treat severe or drug-resistant epilepsy, creates its own vitamin D and bone challenges. A study tracking children on the ketogenic diet found that bone mineral content at the whole body and spine declined steeply, with growth slowing as well. Vitamin D levels and dietary intake of both calcium and vitamin D were suboptimal throughout.22The American Journal of Clinical Nutrition. Progressive bone mineral content loss in children with intractable epilepsy treated with the ketogenic diet The diet restricts many food groups that naturally contain calcium and vitamin D, and the metabolic shift toward ketosis may independently affect bone metabolism.
Children on the ketogenic diet are typically already on one or more anti-seizure medications, so the bone effects stack. Monitoring and supplementation become even more important for this group, and most ketogenic diet protocols now include vitamin D and calcium as standard supplements.
Pregnancy and Epilepsy
Pregnant women with epilepsy face a particular version of this problem. Anti-seizure medications can lower vitamin D in the mother, and those lower levels are reflected in the baby’s cord blood at delivery. An early study of pregnant women on anticonvulsants found that the medications affected vitamin D metabolism and calcium balance during pregnancy, though in women who were vitamin D-supplemented and on low-dose therapy, the disturbances were not clinically severe.23American Journal of Obstetrics and Gynecology. Anticonvulsant drug therapy in human pregnancy: Effects on serum concentrations of vitamin D metabolites in maternal and cord blood
A more recent analysis from the American Epilepsy Society examined outcomes in pregnant women with epilepsy and reported that none of the women with normal vitamin D levels had premature delivery or fetal complications, while among those with low vitamin D, there were seizures during labor, premature deliveries, major congenital malformations, and one intrauterine fetal death.24American Epilepsy Society. Vitamin D Levels and Outcomes in Pregnancy Health in Women with Epilepsy The numbers were small and did not reach statistical significance, but the pattern was concerning enough to reinforce the importance of vitamin D screening during epileptic pregnancies. Of course, low vitamin D may be a marker of overall poorer health rather than a direct cause of worse outcomes, so this remains an area where careful attention to supplementation is prudent even if causation is not proven.
Genetics of the Vitamin D Receptor
There is a genetic angle to this story that gets less attention. Vitamin D works through a receptor (the VDR), and variations in the gene that codes for that receptor differ across populations. A study of children with temporal lobe epilepsy found that certain VDR gene variants were significantly more common in patients than in healthy controls. One variant (the AA genotype of the ApaI polymorphism) was nearly three times as frequent in the epilepsy group, while a protective variant (the AC genotype of FokI) was more common among controls. A particular haplotype spanning multiple VDR variants also carried an increased risk.25PubMed Central. Association between Vitamin D Receptor Gene Polymorphisms with Childhood Temporal Lobe Epilepsy
What this means in practical terms is still unclear. Having a VDR variant that increases epilepsy risk does not necessarily mean that more vitamin D will overcome the problem, because the issue might be how well the receptor functions rather than how much vitamin D is available. But it does suggest that the vitamin D system is biologically intertwined with seizure susceptibility in ways that go beyond simple deficiency and supplementation.
Where Guidelines Stand Today
There are no internationally accepted guidelines specifically for monitoring bone health or vitamin D in people with epilepsy. A 2024 narrative review in Epilepsia proposed a practical monitoring scheme that includes routine vitamin D blood tests for everyone with epilepsy, bone density scans for higher-risk patients (postmenopausal women, people on multiple medications, those with physical disabilities or developmental epileptic encephalopathies), and vitamin D supplementation where deficiency is found.19PubMed. Vitamin D prophylaxis in persons with epilepsy? The review was explicit that there is not enough evidence to justify giving vitamin D supplements to every person with epilepsy as a blanket policy. The recommendation is test-and-treat rather than treat-everyone.
That gap between “plausible benefit” and “proven benefit” can be frustrating for patients. Vitamin D is cheap, widely available, and has a favorable safety profile at standard doses. Many neurologists already check levels as part of routine epilepsy care, even without formal guidelines mandating it. The risk of harm from sensible supplementation is low. The risk of letting vitamin D deficiency persist, particularly for bones, is not.
Sunlight, Seizures, and a Curious Observation
One intriguing finding sits at the edge of this topic. A study analyzing over 1,700 seizures recorded on a dedicated epilepsy ward found that epileptic seizures, particularly complex partial seizures, were less likely to occur on bright, sunny days than on dull, overcast ones. The pattern held even after controlling for seasonal variation, and it did not apply to non-epileptic attacks.26PubMed Central. Seeing the light? Seizures and sunlight Whether this reflects something about light exposure, vitamin D synthesis, circadian rhythms, or simply patient behavior on sunny days is unknown. It is the kind of observation that makes researchers wonder whether the vitamin D connection extends into territory we have not fully mapped yet, while also reminding us how many confounding factors can cloud any single finding in this field.