Too Much Vitamin D: Why Megadoses Raised Falls and Fractures

A single yearly dose of 500,000 IU was designed for a real problem: older women who forget a daily pill. In the randomized trial that tested it, those women fell more and broke more bones, and the harm bunched into the months right after each dose.

That result is the fastest way to understand what too much vitamin D does. It matters most if you already live with chronic pain, because a fall on top of a sensitized nervous system is not a bruise. It is a new injury layered on an old one. In the video for Chapter 10 of The Angry Gut, the book I wrote with Ami Michelle Grimes, I lay out why this molecule is a hormone. Here I want to stay with the dosing trials, because that is where people in pain get hurt.

I am Dr. Gurpreet Singh Padda, MD, MBA, MHP, and for years I filed vitamin D under vitamins and treated a bigger number as a better number. The physiology says otherwise.

Why too much vitamin D backfires

A vitamin is something you eat in small amounts. Vitamin D does not behave like one. Your skin builds it from cholesterol in ultraviolet light, your liver turns it into a storage form, and your kidney and immune cells convert that into the active hormone. Across human target genes, the storage form needs about 322 nM to reach half its effect. The active hormone needs 0.48 nM.

So the thing you swallow and the thing your lab reports are raw material. The body decides how much of it becomes hormone, and it decides with feedback loops.

Here is the part the supplement aisle never prints. A large dose raises fibroblast growth factor 23, a bone-derived signal. That signal turns down the enzyme that activates vitamin D and turns up the enzyme that destroys it. The net result can be too little active hormone sitting behind a report full of storage form. You give more, and the tissue gets less.

The megadose trials a pain patient should know

Start with the annual dose. Among 2,256 older women, falls ran at 83.4 per 100 person-years on vitamin D against 72.7 on placebo. The rate ratio for falling was 1.31 in the first three months after the dose and 1.13 over the following nine. Overall, falls rose by a rate ratio of 1.15 and fractures by 1.26. The median woman started at 49 nmol/L, and fewer than 3% started below 25. These were not deficient women. They were topped up, hard, on a calendar.

Daily dosing is not automatically safe either. Older adults at high risk of falling, who started low, were randomized to different daily doses. Those on 1000 IU or more had more serious falls than those on 200 IU, a hazard ratio of 1.87, and falls ending in a hospital ran at 2.48. The companion analysis found no gain in walking speed, chair stands, grip strength or the six-minute walk.

Then bone itself. Over three years, 10,000 IU a day lowered forearm bone density by 7.5 mg HA/cm3 against 400 IU, and 4000 IU lowered it by 3.9. Blood levels in the highest arm climbed to 188 nmol/L at three months and then fell to 144 on the same dose. The body had adapted. Bone strength did not differ significantly, so this is a density signal, not a fracture count.

What a fall costs a nervous system already in pain

For someone with spinal pain, neuropathy or a sensitized nervous system, a fall can cost months: guarding, less movement, worse sleep, and a brain that relearns to expect pain. That is why a harm signal in older adults carries more weight in a pain practice than a null benefit does.

The largest monthly-dose trial adds a sober note. In 21,315 Australians aged 60 and over, 60,000 IU a month for five years pushed levels to 115 nmol/L against 77 on placebo. All-cause mortality did not move, at a hazard ratio of 1.04. Cancer mortality leaned the wrong way at 1.15, and once the first two years of follow-up were set aside it reached 1.24, with an interval that excluded one. The investigators wrote that this regimen might not be appropriate for people who are already replete.

The drivers stack. Biologically, a governed hormone adapts to excess by destroying it, and the storage form piles up without adding much signal. Behaviorally and economically, the market sells certainty: bottle labels promising thousands of genes, once-a-year dosing that is convenient for a pharmacy schedule, and the cultural reflex that more of a good thing must be better.

This is the same pattern I see with metabolic inflammation and chronic pain: the system rewards the fast fix and ignores the regulation underneath it.

Where vitamin D does earn its place

If megadoses hurt and fracture trials were flat, why bother? Because the receptor’s program is immune, not skeletal. Mapped across the genome, the receptor occupies 2,776 positions but changes only 229 genes, and those binding sites cluster near genes tied to autoimmune disease.

That shows up in people. In 25,871 midlife and older adults, supplementation did nothing for total fractures, a hazard ratio of 0.98. The same trial cut new autoimmune disease by about 22% over five years: 123 cases against 155, a hazard ratio of 0.78. The conditions it counted included rheumatoid arthritis, polymyalgia rheumatica, autoimmune thyroid disease and psoriasis. Several of those arrive at a pain clinic first.

For readers whose pain has an autoimmune thread running through it, that is the result worth knowing.

The patients who genuinely run low

Too much and too little are both real. The people who run low tend to share a terrain problem, not a willpower problem. In inflammatory bowel disease, the odds of deficiency were 1.85 with active disease and 1.61 with steroid exposure. The largest odds ratio in that analysis was not a disease variable at all: non-Caucasian patients carried 3.79.

Skin explains part of that. Keeping 97.5% of dark-skinned people at high latitude above 50 nmol/L through winter takes roughly 2,672 IU a day, far above intake tables that were built mostly from light-skinned volunteers. Extra body fat holds the molecule and lowers what circulates. And we moved a species that makes this hormone in sunlight indoors, behind glass, onto night shifts. That is why I prescribe daylight as part of pain treatment: skin synthesis delivers a steady daily supply the body can regulate, rather than one surge it has to defend against.

A bowel that cannot absorb fat-soluble molecules is the extreme version, and it leads straight into the next chapter’s question of what crosses a damaged gut. I take that up in how the gut reaches the spine. The blood supply behind it is in a gut starved of oxygen.

Dosing a hormone like a hormone

This is the practice’s position. We test when there is a reason: malabsorption, bowel surgery, steroid exposure, darker skin at our latitude, obesity, or an autoimmune pattern. We replace daily rather than in large intermittent doses, because the bolus trials produced harm. We correct the deficit and stop, because the dose-response flattens and the axis fights back.

No trial has tested vitamin D dosing targets in malabsorbing patients, so that part rests on mechanism and on the harm data above, applied to the person in front of us. The guideline that recommends against routine testing was written for people with no established indication. Many of our patients have one.

Hypervitaminosis shows up above 100 ng/mL and toxicity above 150, but the bone-density trial shows harm well below that. Work out any change with the physician who knows your labs and your medication list; do not adjust it on your own.

Every study named here, with its full numbers and what each one cannot show, is collected in the Chapter 10 Deep Dive, along with the questions worth asking at your next visit.

Frequently asked questions

How much vitamin D is too much?

Hypervitaminosis tends to appear above 100 ng/mL, and outright toxicity above 150. But harm starts well before toxicity. In a three-year trial, 10,000 IU a day lowered forearm bone density against 400 IU, and a single 500,000 IU yearly dose raised falls and fractures in older women. The right amount is set by your deficit and your absorption. We cover the quieter deficiencies in magnesium, vitamin D and B vitamins in nerve pain.

Can taking vitamin D make you more likely to fall?

In older adults, yes, depending on dose and schedule. A yearly megadose raised the falling rate most in the three months after dosing. In a separate trial of people already prone to falling, 1000 IU a day or more produced more serious falls than 200 IU, with no gain in strength or walking speed. If falls are already a concern, balance and fall-risk testing measures that risk directly.

Is a weekly or yearly high dose of vitamin D better than a daily dose?

The evidence favors daily. A large dose raises fibroblast growth factor 23, which slows activation of vitamin D and speeds its breakdown, so a surge can leave less active hormone than a steady supply. The annual megadose trial showed harm clustered right after dosing. Dosing schedules belong in the same review as the rest of your medications, the way we approach medication lists and fall risk in older adults.

Does vitamin D help with autoimmune pain conditions?

It may help prevent them. In a five-year trial of 25,871 midlife and older adults, daily supplementation cut new autoimmune disease by about 22%, including conditions like rheumatoid arthritis, polymyalgia rheumatica and psoriasis. It did not reduce fractures in the same people. That split points to an immune program, not a bone one. The immune side of the story continues in why your immune system is not confused.

Why is my vitamin D still low when I take a supplement?

Absorption, skin and body composition all bend the number. Active bowel disease and steroid exposure both raised the odds of deficiency in inflammatory bowel disease, and darker skin at northern latitudes can require far more than standard intake tables suggest. Extra body fat also holds the molecule out of circulation. A gut lining that is not absorbing well is its own problem, covered in what a leaky gut test cannot see.

Sources

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Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP, board certified in anesthesiology, pain medicine, interventional pain management, addiction medicine and obesity medicine. Adapted from Chapter 10 of The Angry Gut by Dr. Padda and Ami Michelle Grimes. Last reviewed September 2026.

Dr. Gurpreet Singh Padda, MD, MBA, MHP