Vitamin D, Sunlight, and Sleep: More

In the comments on yesterday’s post  (“Can Vitamin D Replace Sunlight? A Stunning Discovery”), two commenters (John and Aaron Blaisdell) noted that Nephropal had said something similar. They’re right. Here’s what Nephropal said in 2009:

Vitamin D taken at night causes insomnia. This is a complaint of a few of my patients. Moreover, when they switch to morning dosing, the insomnia subsides. Thus, Vitamin D should be taken in the morning.

That’s a great observation,  but not the same as Primal Girl’s. Here is her observation, shortened for clarity:

 I usually took my supplements mid-afternoon. I vowed to take them first thing every morning. I tried it the next day and that night I slept like a rock. And the next night. And the next.

The two observations support each other. Both support the idea that the timing of Vitamin D matters. But there are also big differences. Paleo Girl had been taking her Vitamin D in mid-afternoon, not at night. She shifted to first thing in the morning, which is more specific than morning. I changed the title of yesterday’s title to make clearer what is new here: the idea that Vitamin D can substitute for sunlight.

Lots of things cause insomnia if you take them in the evening. Caffeine and other stimulants, for example. A comment on yesterday’s post said that B vitamins and calcium cause insomnia if taken in the evening. This is why Nephropal’s observation, although very important, is not a stunning surprise. You stop taking X in the evening, your sleep improves — I won’t be astonished, no matter what X is.

Vitamin D is not a stimulant or is at best a mild stimulant. Taking Vitamin D in the afternoon should not cause trouble sleeping. Yet Primal Girl had trouble sleeping. And she was getting little morning sunlight. It is a real insight that first-thing-in-the-morning Vitamin D could have the same effect as first-thing-in-the-morning sunlight — in other words, could substitute for missing sunlight. Against all odds, the results supported this idea.

One commenter on yesterday’s post said Primal Girl’s results were both unproven and obvious. Vitamin D is technically a hormone! Melatonin is a hormone, said the comment. I have not heard anyone propose taking melatonin first thing in the morning to improve sleep. It is standard to take melatonin in the evening. The accepted view among circadian rhythm researchers is that sunlight produces its effects on circadian rhythms via nerves, not blood. For example, hundreds of experiments have found that destroying the suprachiasmatic nucleus of rats destroys their circadian rhythms. The suprachiasmatic nucleus receives neural input from the eyes — that’s why these lesions were first made (by Irv Zucker, a Berkeley colleague of mine).

Lots of people think Vitamin D improves sleep. That’s not new. Here’s what one of them said, in a post promisingly titled “When is the best time to take your Vitamin D supplement?“:

In an effort to boost absorption of vitamin D, individuals were asked to take their vitamin D supplements with the largest meal of the day. After 2-3 months, vitamin D levels were checked again.At the end of the study period, vitamin D levels had risen to an average of 47.2 ng/ml (118 nmol/l) – an average increase in vitamin D levels of about 57 per cent. . . It seems sensible, I think, for individuals who are currently supplementing with vitamin D to take this with their largest evening meal.


19 Replies to “Vitamin D, Sunlight, and Sleep: More”

    1. no, not familiar, thanks. I downloaded it. It is full of attitudes that I think make progress more difficult (e.g., the idea that some evidence should be ignored). Maybe I will blog about it.

  1. I’m a little confused. I understand the claim to be: Vitamin D first thing in the morning helps you sleep better at night.

    Now here’s the sequence of events as I see it:
    1. Primalgirl has been sleeping poorly
    2. She was and had been taking Vitamin D3 for a while
    3. At night.
    4. She then started taking it first thing in the morning
    5. Starts sleeping like a rock

    BUT, crucially, she also says: “Days I forgot and skipped the D3, I still slept great.”

    So it sounds like the Vitamin D at night was interfering with her sleep, and now it’s been taken away and hence no more interference. If the D3 in the morning was actually helping her sleep better (than baseline) then she should sleep poorly (less better) on the days she skips it.

    Or am I missing something?

    1. “Am I missing something?” Yes. She usually took the Vitamin D in mid afternoon, not night. Unlikely that she slept poorly because her afternoon Vitamin D was interfering with her sleep. It might be true that although she usually took her Vitamin D in the afternoon, perhaps once/week she took it in the evening and that was enough to keep her from getting a high-amplitude (= powerful) circadian rhythm in her sleep/wake oscillator. An oscillator doesn’t require constant (e.g., daily) input to work properly. You don’t have to push a swing every oscillation to make it keep swinging in a big arc. A few pushes at the right time can have a powerful and long lasting effect. A few pushes at the wrong time can be very damaging. So perhaps she was damaging her sleep every night by once/week taking her Vitamin D at night. And once she started doing the right thing (taking her Vitamin D at a favorable time, morning, rather than a neutral time, afternoon) everything started working great.

    1. MetaThought, thanks for the link. You are correct that I have studied the connection between animal fat (pork fat) and sleep. My first self-experiment of any consequence was about acne.

  2. lunchtime might be best?

    J Bone Miner Res. 2010 Apr;25(4):928-30.
    Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D.
    Mulligan GB, Licata A.

    “Many patients treated for vitamin D deficiency fail to achieve an adequate serum level of 25-hydroxyvitamin D [25(OH)D] despite high doses of ergo- or cholecalciferol.”

    “Thus it is concluded that taking vitamin D with the largest meal improves absorption and results in about a 50% increase in serum levels of 25(OH)D levels achieved.”

    PMID: 20200983

    1. donat, what about sleep? Percent absorbed is not a big deal — no need to maximize it. If you want more Vitamin D in your blood you need only take more Vitamin D. It isn’t expensive.

  3. ouch, sorry. I was reacting to your earlier post where this aspect was not yet remarked on. The point was simply that one needs to be aware that dosage might be timing/food dependent.

  4. Seth, I recently found your book on Amazon while searching for a book to help me improve my sleep . . . just ordered it and can’t wait to start reading it. Very interested to know the principles laid out in the book and will definitely try the diet. Re: vitamin D, i am taking vit D3 with my first meal of the day but when too busy it’s not until noon I get to do it . . . I am wondering if taking it first thing in the morning mean taking it on an empty stomach. Since I can’t eat until around 11-12 noon I wanted to know if it is safe to take Vit D or any other supplement on an empty stomach. Thank you.

  5. this entire exchange surprised me because i started taking 5000 IU of vitamin d before bed and slept 10 hours both nights since, so i expected to find people saying it helped them sleep by taking it before bed

    1. this entire exchange surprised me because i started taking 5000 IU of vitamin d before bed and slept 10 hours both nights since, so i expected to find people saying it helped them sleep by taking it before bed

      you’ve only taken it two nights?

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