Vitamin D supplementation is a great option for people who don’t have access to year-round sun, but a lot of people are confused about when to take their vitamin D supplement.

Although widely available from both sunshine and food sources, vitamin D deficiency is estimated in more than 50% of the American population.1 It can cause major health problems if not addressed, affecting everything from immune health and mood to bone strength and, yes, even sleep.

Unless you’re getting regular sun exposure, taking a vitamin D supplement can protect you from encountering a deficiency.

However, there’s a lot of chatter about when to supplement. So, we’re clearing the air and giving you what you need to know about when the most ideal time to take vitamin D is.

What Is Vitamin D?

Although vitamin D is classified as a fat-soluble vitamin—along with vitamins A, E, and K—this vitamin functions more as a hormone, playing key roles in bone development and metabolism by regulating levels of calcium, magnesium, and phosphate.1

A circulating vitamin D concentration of 30 ng/mL is required to maintain healthy levels. When serum concentrations drop below that, it can lead to a variety of health complications if not addressed immediately.

Aside from its role in supporting bone metabolism, vitamin D is also involved in:

  • Weight management
  • Immune function
  • Mood
  • Inflammation

The functions of vitamin D span quite a range of systems, which means that maintaining sufficient levels is crucial.

However, sun exposure to boost levels can be hard to come by depending on where you live, your schedule, and what time of the year it is.

Even if you are lucky enough to have sun, things like sunscreen use, clothing, and skin color can all influence how much vitamin D your body naturally produces.2

Why Should People Supplement Vitamin D?

Weight loss

While it’s not likely that bumping up your intake of vitamin D is going to move the scale needle by any huge amount, research does support an indirect role for vitamin D in weight loss.

A study published in the British Journal of Nutrition found that overweight or obese women who combined calcium and vitamin D supplementation shed more weight than those who took a placebo.3

This may be attributed to the appetite-suppressing effect of the calcium and vitamin D combination.

Supports mood

If your mood has ever taken a nosedive in the winter due to lack of sunshine, you’ve seen the effects of low vitamin D first hand.

That’s partially because vitamin D is involved in the biosynthesis of serotonin—a neurotransmitter responsible for regulating mood.

It activates tryptophan hydroxylase 2, an enzyme responsible for turning tryptophan into serotonin.4

It’s suggested that the omega-3 fatty acids EPA and DHA also increase serotonin release from presynaptic neurons by reducing E2 series prostaglandins. They also influence serotonin receptor action by increasing cell membrane fluidity in postsynaptic neurons.

As such, insufficient levels of vitamin D, EPA, or DHA can result in dysfunctional serotonin activation and function, which may contribute to mood imbalances or disorders.

Improves immune function

Vitamin D is a big one for the immune system because of its role in supporting both the innate and adaptive branches of immunity.

Together, these systems work to protect the body against invading pathogens. Low vitamin D levels have been linked to an increased risk of autoimmunity and increased susceptibility to infection.5

It also helps to tamper down inflammation by decreasing the production of inflammatory cytokines (IL-17, IL-21) and inhibiting monocyte production inflammatory cytokines such as IL-1, IL-6, IL-8, IL-12, and TNFα, on top of enhancing the production of anti-inflammatory cytokines like IL-10.6

Strengthens bones

Want stronger and healthier bones? It’s not all about calcium.

While calcium and phosphorus usually steal the spotlight where bone health is concerned, without vitamin D, calcium and phosphate aren’t much use.

That’s because calcium acts on intestinal epithelium to stimulate uptake of calcium from the gut, along with interacting with parathyroid hormone (PTH) to enhance reabsorption of calcium and phosphate in the kidneys into the blood.

As a result, it plays a key role in supporting the mineralization of the collagen matrix in bone to maintain optimal bone mineral density.5, 7

What Is The Best Time To Take Vitamin D?

The most “optimal” time to take supplements is a big topic of debate. Some are better than in the morning on an empty stomach; others are best with meals; while others should be taken before bed.

But what about vitamin D—when is the best time to take it?

For most people, taking vitamin D at any point during the day isn’t a big issue, but there is one major factor that can dictate its efficacy—what you’re taking it with.

Vitamin D is a fat-soluble vitamin, so if you’ve been knocking back your vitamin D on its own, chances are you’re not absorbing much of it. For the body to absorb vitamin D, it requires the presence of dietary fat.

One small study of 17 people found that supplementing vitamin D with the largest meal of the day enhanced serum concentrations of vitamin D by roughly 50% after just 2–3 months.8

Another study showed that consuming vitamin D alongside a high-fat meal (30% fat) increased vitamin D blood levels by 32% after 12 hours compared to a fat-free meal.9

For some people, taking vitamin D in the early evening or before bed can interfere with sleep, while for others it has minimal effect.

However, if you’re relying on a supplement that contains other ingredients besides vitamin D, it’s recommended to take it early in the day.

A supplement like Pre Lab Pro that contains 500 IU (12.5mcg) of vitamin D provides a modest serving, but it also contains caffeine, which, if taken at night, has a pretty good chance of interfering with your sleep.

Let’s see why.

Vitamin D And Sleep

The last thing you want is to take your vitamins at the wrong time, only to have them keep you up the whole night. Along with the B vitamins, vitamin D is one of the nutrients that shouldn’t be taken in the evening hours due to its impact on sleep.

Vitamin D receptors and the enzymes responsible for controlling their activation and degradation are expressed in several different regions of the brain, including those involved in sleep regulation.10

Vitamin D and sleep are a double-edged sword. Sufficient levels of vitamin D are required to promote good quality sleep, but taking vitamin D at the wrong time can have an inverse relationship with the hormones that control sleep.

Research shows that vitamin D is involved in the pathway for the biosynthesis of melatonin, the hormone involved in regulating human circadian rhythms and sleep.10

When vitamin D helps convert tryptophan into 5-hydroxytryptophan (5-HT), it's further metabolized to serotonin and then to melatonin11.

Some research suggests that elevated levels of vitamin D throughout the day may act as a signal to suppress the production of melatonin, thereby interfering with sleep onset.12

What’s more, there’s mounting evidence suggesting that low vitamin D levels increase the risk of sleep disturbances and people with low levels tend to have poorer sleep quality and reduced sleep duration.13-15

One study found that people who increased their intake of vitamin D experienced improvements in neuralgic symptoms and sleep; they show that vitamin D targets neurons in the diencephalon and several brainstem nuclei to elicit direct central effects on sleep.16

Final Thoughts

The entire picture of how vitamin D interacts with areas in the brain that regulate sleep isn’t known, but what we do know is this—get enough.

But make sure you’re taking it in the morning or early afternoon to avoid sleep disruptions. Other supplements that are great for supporting sleep are magnesium, L-theanine, and tryptophan, all of which can be taken closer to bedtime.


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