You've probably heard that spending time in the sun givesyou all the vitamin D you need. Your doctor may have also told you that yourvitamin D level is "normal." Unfortunately, both of these commonreassurances can be misleading and can lead to serious health problems.
Over the past 20 years, I’ve written over 1,000 blog postson our NYHeadache.com site, and a dozen of those posts were devoted to vitaminD. This is a compilation of those posts, plus many more recent studies ofvitamin D.
Why you should get your vitamin D level checked
Vitamin D deficiency is one of the most common, most overlooked, and mosteasily correctable health problems in the world. It affects your bones, immunesystem, brain, heart, and headaches. Yet most people have never had their levelchecked, and many who have were falsely reassured by a result that their labcalled "normal."
I believe every person should know their vitamin D number, just as they knowtheir cholesterol or blood pressure. It's a simple, inexpensive blood testcalled 25-hydroxyvitamin D (25(OH)D), and the information it provides canchange the course of your health. If your doctor hasn't ordered it, ask for it.And when you get the result, don't just accept "normal." Here’s why.
Most of us are vitamin D-deficient and don't know it.
Vitamin D deficiency is one of the most common nutritional deficiencies in theUnited States. A large analysis of over 71,000 Americans found that roughly 1in 4 had levels below what even the most conservative guidelines consideradequate, and nearly two-thirds had levels below what many experts consideroptimal. The problem is especially pronounced among Black Americans, peoplewith darker skin, those who are overweight, and anyone who spends most of theirday indoors, which in modern life is most of us.
Why the sun isn't enough
The sun was historically our main source of vitamin D. Whenultraviolet B (UVB) rays hit your skin, they trigger the production of vitaminD3. But modern life has changed the equation dramatically.
Several factors work against you:
- Where you live matters. If you live above the 33rd parallel, whichincludes most of the United States, all of Canada, and most of Europe, thesun's UVB rays are too weak from roughly November through March to producemeaningful vitamin D in your skin, no matter how long you're outside.
- Sunscreen blocks vitamin D production. Sunscreen with SPF 15 blocksapproximately 99% of the skin's ability to make vitamin D. And of course,dermatologists rightly recommend sunscreen to prevent skin cancer.
- We live indoors. Most Americans spend the vast majority of their dayinside offices, homes, and cars. Glass windows block UVB rays entirely.
- Skin color matters. Darker skin contains more melanin, which acts as anatural sunscreen. A person with dark skin may need up to six times more sunexposure to produce the same amount of vitamin D as someone with light skin.
- Age works against you. A 70-year-old produces about 75% less vitamin Dfrom the same sun exposure as a 20-year-old.
- Weight matters too. Vitamin D is fat-soluble, meaning it gets trappedin body fat. People with obesity have significantly lower circulating vitamin Dlevels even with the same sun exposure or supplement intake.
Even in sunny climates, studies have found high rates of vitamin D deficiency,which proves that sunshine alone is not a reliable strategy. One of my patientsin his early 20s lived full-time in the Bahamas, but was still deficient.Another young man in his late 20s was a boat captain, and he was alsodeficient.
The "normal" range is dangerously misleading.
This is the single most important point in this entire post,and the reason I chose the title I did.
When your doctor checks your vitamin D level, the lab report typically flagsanything above 20 ng/mL as "normal." The standard reference range onmost lab reports is 20 to 100 ng/mL (sometimes 30 to 100 ng/mL). That's anenormous range. Imagine if your doctor told you your blood pressure was"normal" anywhere between 90/60 and 200/120. You'd rightly questionthat. Yet that's essentially what happens with vitamin D.
The critical problem is that 21 ng/mL and 60 ng/mL are both labeled"normal," but they are not the same. A person at 21 is barelyscraping by. A person at 60 is thriving. The science increasingly shows thatthe health benefits of vitamin D (protection against cancer death, autoimmunedisease, bone fractures, respiratory infections, and migraines) are seen atlevels well above the bare minimum of 20.
Different expert groups can't agree on what level is truly sufficient:
- The National Academy of Medicine (formerly the Institute of Medicine) says 20ng/mL is adequate for most people.
- The Endocrine Society says you need at least 30 ng/mL, and that 20 to 29ng/mL is "insufficient."
- Many vitamin D researchers, including Dr. Michael Holick, one of the world'sleading vitamin D experts, recommend a target range of 40 to 60 ng/mL formaximum health benefits.
So if your level comes back at 22 ng/mL, your lab report will say"normal," but by the Endocrine Society's standards, you'reinsufficient. By many researchers' standards, you're well below optimal.
My recommendation: aim for at least the middle of the normal range, 40-50ng/mL. Don't settle for a level that barely clears the lowest bar. Thedifference between 25 and 50 could be the difference between "technicallynot deficient" and actually reaping the health benefits that vitamin Dprovides. In my practice, I aim for levels of at least 40 ng/mL in all mypatients, and I've seen meaningful improvements, particularly in headachefrequency, when patients move from the low end of "normal" to themiddle or upper range.
Vitamin D and headaches
As a headache specialist, I regularly see the connectionbetween vitamin D and migraines. Studies have found that 45 to 100% of migrainepatients have vitamin D deficiency or insufficiency. Research has shown thatvitamin D levels tend to correlate negatively with headache frequency: thelower your vitamin D levels, the more headaches you may get.
Multiple clinical trials have demonstrated that vitamin D supplementation at1,000-4,000 IU per day can reduce the frequency of migraine attacks. Ameta-analysis of randomized controlled trials found that vitamin Dsupplementation significantly reduced headache days, headache frequency,headache severity, and migraine disability scores compared to placebo.
This doesn't mean vitamin D is a cure for migraines. But correcting adeficiency may be one of the simplest and safest things you can do to reduceyour headache burden.
Vitamin D, gum health, and your heart and brain
Here's one you might not expect: vitamin D plays an important role in thehealth of your gums. A large national study found that Americans with thehighest vitamin D levels had 20% less gum bleeding than those with the lowestlevels. A randomized controlled trial showed that vitamin D supplementationreduced gum inflammation in a dose-dependent manner, with patients taking 2,000IU daily seeing improvement within just one month. I recently had a patientwhose bleeding gums improved dramatically after correcting a vitamin Ddeficiency, which is consistent with research findings.
Why does this matter beyond your mouth? Because gum disease is now recognizedas a significant risk factor for heart disease, stroke, and even dementia. A2025 scientific statement from the American Heart Association confirmed thatperiodontal disease is independently associated with atheroscleroticcardiovascular disease. Bacteria from infected gums can enter the bloodstream,trigger systemic inflammation, promote endothelial dysfunction, and acceleratethe buildup of arterial plaque. A meta-analysis of 39 cohort studies involvingover 4 million people found that periodontal disease was associated with a 24%increased risk of major cardiovascular events, a 26% increased risk of stroke,and a 42% increased risk of cardiac death. The same oral bacteria, particularlyPorphyromonas gingivalis, have been found in atherosclerotic plaques in theheart and brain.
The brain connection is equally concerning. Multiple meta-analyses have foundthat periodontal disease is associated with increased risk of both cognitivedecline and dementia. Periodontal pathogens can reach the brain through thebloodstream or even along nerve pathways, and research has linked them toincreased production of the amyloid plaques seen in Alzheimer's disease.
So by keeping your vitamin D levels adequate, you may be protecting not justyour gums, but also your heart and your brain. It's a chain reaction: vitamin Dreduces gum inflammation; healthier gums mean less chronic infection enteringyour bloodstream; and less systemic inflammation means a lower risk ofcardiovascular and cerebrovascular disease. Few supplements offer that kind ofcascading benefit.
What the Latest Research Shows
In the past few years, several major studies and guidelineshave reshaped our understanding of vitamin D's role beyond bone health.
Multiple sclerosis. The link between vitamin D and multiple sclerosis(MS) is one of the most compelling in all of medicine. It has long beenobserved that MS is more common the farther you live from the equator, apattern that mirrors the geography of vitamin D deficiency. Studiesconsistently show that people with MS have significantly lower vitamin D levelsthan healthy individuals, and that lower levels are associated with morerelapses, more brain lesions on MRI, and greater disability.
The evidence has now moved beyond observation. A large Norwegian study of over78,000 women found that higher vitamin D intake was associated with a 42% lowerrisk of developing MS. This was in Norway, where the sun is too weak forvitamin D production most of the year, strongly suggesting that vitamin Ditself, not just sun exposure, is protective. The landmark D-Lay MS trial,published in JAMA in 2025, was a game-changer: high-dose vitamin D given as astandalone treatment to patients after their first MS-like episode reduceddisease activity by 34% compared to placebo, an effect comparable to someprescription MS drugs. Patients who benefited most were those with the mostsevere vitamin D deficiency. A comprehensive 2025 meta-analysis of 40 studiesconfirmed that MS patients have significantly lower vitamin D levels thanhealthy people, and that high-dose vitamin D supplementation significantlyreduces relapse rates.
The bottom line: maintaining adequate vitamin D levels may help prevent MS and,for those who already have it, reduce disease activity, especially when levelsare raised from deficient to sufficient.
COVID-19. During the pandemic, vitamin D became one of the most studiednutrients in relation to COVID-19, and the findings are striking. A massivemeta-analysis of 76 studies involving nearly 2 million adults found that peoplewith vitamin D deficiency had about twice the odds of dying from COVID-19 andnearly twice the odds of developing severe disease compared to those withadequate levels. Another systematic review found that patients who were takingvitamin D supplements had a 65% lower risk of severe COVID-19 and a 65% lowerrisk of dying from it. A large study of U.S. veterans found that vitamin Dsupplementation was associated with a 28% reduction in COVID-19 infection and a33% reduction in 30-day mortality, with the greatest benefits observed amongthose with the lowest vitamin D levels and among Black veterans.
A meta-analysis of 25 randomized controlled trials found that vitamin Dsupplementation significantly reduced ICU admissions and the need formechanical ventilation in COVID-19 patients, and reduced mortality specificallyin patients who were vitamin D deficient. While some individual trials did notshow a benefit, particularly when vitamin D was given after infection hadalready progressed, the overall weight of evidence strongly suggests thathaving adequate vitamin D levels before you get sick offers meaningfulprotection against severe outcomes.
This is not to say that vitamin D is a treatment for COVID-19. But it is yetanother powerful reason to make sure your levels are where they should bebefore the next infection hits.
Cancer mortality. Daily vitamin D supplementation appears to reduce therisk of dying from cancer by about 12%, according to a large meta-analysis of14 randomized controlled trials involving over 100,000 people. The landmarkVITAL trial, which followed over 25,000 Americans taking 2,000 IU of vitamin Ddaily for more than five years, found a promising signal for reduced cancerdeath, especially after the first two years. Importantly, this benefit was seenwith daily dosing, not with large, infrequent "mega-doses."
Autoimmune diseases. The VITAL trial also found that vitamin D andomega-3 fatty acid supplementation together reduced the incidence of autoimmunediseases. Genetic studies (called Mendelian randomization studies) have foundevidence supporting a causal link between higher vitamin D levels and lowerrisk of certain autoimmune conditions, particularly psoriasis and possiblylupus.
Diabetes prevention. For people with prediabetes, the 2024 EndocrineSociety guidelines now recommend considering vitamin D supplementation toreduce the risk of progressing to type 2 diabetes, a significant newrecommendation backed by moderate-certainty evidence.
Mortality in older adults. For adults over 75, the evidence is nowstrong enough for the Endocrine Society to recommend routine vitamin Dsupplementation to reduce the risk of all-cause mortality.
Pregnancy. Vitamin D supplementation during pregnancy may reduce therisk of preeclampsia, preterm delivery, and other complications. The averagedose used in clinical trials was about 2,500 IU daily, far more than the 400 to600 IU found in most prenatal vitamins.
Respiratory infections. In children and adolescents, vitamin Dsupplementation has been associated with fewer upper respiratory tractinfections.
Here's my practical advice:
1. Get your level checked. Ask your doctor for a 25-hydroxyvitamin Dblood test. Don't just accept "normal." Ask for the actual number.
2. Aim for the middle of the range, not the bottom. A level of 40 to 60ng/mL is where the science suggests the greatest benefits lie. If your level isin the 20s or low 30s, you have room and reason to improve.
3. Supplement wisely. Most adults need at least 1,000 to 2,000 IU ofvitamin D3 (cholecalciferol) daily to maintain adequate levels. Some people,especially those who are overweight, older, have darker skin, or haveabsorption issues, may need significantly more. Vitamin D3 is preferred over D2because it raises blood levels more effectively and sustains them longer. Up to5,000 IU daily is considered safe for most adults, but some need more.
4. Don't rely on the sun alone. Enjoy the outdoors, but understand thatfor most people, most of the year, sun exposure cannot provide enough vitaminD.
5. Don't rely on food alone either. Very few foods naturally containsignificant vitamin D. Oily fish (like salmon and mackerel), egg yolks, andfortified milk or orange juice provide some, but not nearly enough for mostpeople.
6. Daily is better than mega-doses. The research consistently shows thatdaily vitamin D supplementation is more effective and safer than taking largedoses weekly or monthly. In fact, some studies have found that high-doseintermittent supplementation may actually increase the risk of falls.
7. Recheck your level. After starting supplementation, have your levelrechecked in 2 to 3 months to make sure you've reached your target. Vitamin Dis very safe, but levels well above 100 ng/mL can cause problems, so monitoringis important.
