Snooze University

Can Too Much Vitamin D Cause Insomnia?

by Dale Cudmore | Updated: Jul 21, 2021

Even though vitamin D is generally a good supplement for sleep, recent studies show that it is possible to have sleep troubles or even insomnia if you get too much vitamin D.

It’s almost impossible to get too much just from the sun, but when you add in supplements, it’s fairly easy.

The underlying question is how much vitamin D is too much?

In Theory, Vitamin D Supplementation Should Help Sleep

Vitamin D deficiency is incredibly common. There are likely over 1 billion people worldwide that are significantly deficient in it (1).

There’s a lot of research on vitamin D deficiency that shows it can cause all sorts of issues, including those related to sleep:

  • Vitamin D deficiency is known to cause sleep apnoea (1).
  • Low vitamin D levels are associated with higher odds of short sleep duration (2).
  • Low vitamin D levels are seen in adults with longer time to fall asleep (3).

A 2 year study found that vitamin D supplementation improved the sleep of most people with a deficiency (4).

SummaryFor people with a vitamin D deficiency, supplementation can improve sleep issues. However, it’s still important to not get too much.

Sleep Side Effects of Too Much Vitamin D

What can happen is that someone suspects they have low vitamin D levels, and then they start taking high dose vitamin D3 supplements (4,000 IU+) on a daily basis.

Since vitamin D is a fat soluble vitamin (i.e. excess is stored in body fat, rather than being flushed out), it can build up to dangerous levels. Vitamin D intoxication is rare, but it does happen, and can be dangerous (5).

But even if your vitamin D levels don’t get to those dangerous levels, it can still be high enough to cause some issues.

For example, one study found (6):

Vitamin D supplementation of 2000 IU/d may result in overall worse sleep quality for postmenopausal women with low circulating vitamin D undergoing weight loss.

There’s not as much research on having too much vitamin D compared to deficiency, but it does seem like having high levels of vitamin D can cause sleep issues.

How Much Vitamin D Is Optimal For Health and Sleep

The NIH has set a tolerable upper intake for vitamin D at 600 IU per day, including vitamin D from sun exposure (7).

Other experts recommend a slightly higher amount:

Most experts agree that 1,000 IU of vitamin D3 is required if there is no exposure to sunlight (8).

Either way, unless you’re under doctor’s orders, having a 5,000 IU supplement per day is overkill and can be detrimental to your health.

Instead, have a capsule once every 5 days or so (if it contains 5,000 IU).

SummaryIf you’re getting no sunlight, 600-1,000 IU of vitamin D3 is generally recommended by health experts. If you’re getting sunlight, you need even less.

When You Take a Vitamin D Supplement Can Affect Insomnia

While the research isn’t conclusive, I’ve read some studies that suggest that when you take a vitamin D supplement may be as important as dosage.

Melatonin is arguably the most important hormone when it comes to getting to sleep and sleeping well.

A 3 month study on vitamin D supplementation found that (9):

After 3 months supplementation, vitamin D levels increased and nighttime melatonin secretion decreased significantly in the high dose group, but not in the low dose group.

For reference, the “low dose” group here had 800 IU per day, while the “high dose” group had 4,370 IU per day.

So the dosage does matter.

But the study also suggests that there’s a relationship between vitamin D and melatonin production.

It’s not that surprising, since light (particularly sunlight) suppresses melatonin production.

SummaryAgain, there’s not much research published in this area, but it’s possible that taking a vitamin D3 supplement close to bed time could inhibit melatonin production and make it hard to get to sleep.


  1. Understanding vitamin D deficiency
  2. Vitamin D and actigraphic sleep outcomes in older community-dwelling men: the MrOS sleep study
  3. Low vitamin D levels in adults with longer time to fall asleep: US NHANES, 2005-2006
  4. The world epidemic of sleep disorders is linked to vitamin D deficiency
  5. Vitamin D Toxicity-A Clinical Perspective
  6. Repletion of Vitamin D associated with deterioration of sleep quality among postmenopausal women
  7. Vitamin D - Fact Sheet for Health Professionals
  9. The influence of vitamin D supplementation on melatonin status in patients with multiple sclerosis

