While sleep hygiene, stress and screen time often take centre stage in conversations about sleep quality, emerging research is shining a light on a lesser-known factor: vitamin D.

One of the 13 essential vitamins our bodies need to function properly, It helps to promote calcium absorption, supporting healthy bones and teeth, and also plays a key role in maintaining the immune system, nervous system and muscle health.

There are two main types of vitamin D: D2 and D3. Vitamin D2 is obtained through the digestion of certain foods and dietary supplements. Vitamin D3, while also available through diet, is also naturally produced by the skin when exposed to sunlight.

The role of vitamin D in serotonin and dopamine regulation:

Vitamin D regulates the expression of tryptophan hydroxylase 2, an enzyme critical for the production of serotonin. “Serotonin plays a pivotal role in sleep onset and maintaining sleep architecture.” Says Dr. Bruni.

“Furthermore, dopamine, another neurotransmitter influenced by vitamin, plays a role in wakefulness and motor control, both of which are relevant in disorders such as restless legs syndrome.”

Research suggests that it can influence both the production and release of dopamine, and a deficiency may contribute to dopamine dysfunction.

Dr. Bruni suggests that it’s role in regulating these neurotransmitter systems means the nutrient “may influence circadian rhythm entrainment, mood regulation, and the sleep-wake cycle.”

“The dysregulation of serotonin and dopamine systems has also been implicated in insomnia and other sleep disorders.”

Vitamin D, circadian rhythms and sleep stages:

“Vitamin D receptors are widely distributed throughout the brain, including regions critical for sleep regulation such as the hypothalamus, prefrontal cortex, substantia nigra, and hippocampus,” says Dr. Bruni.

One of the most important regions for sleep regulation is the hypothalamus, specifically the suprachiasmatic nucleus, which acts as the body’s master clock, central to circadian rhythm regulation. The presence of vitamin D receptors in these brain regions suggests that the nutrient may have a key influence on the regulation of sleep-wake cycles.

Additionally, studies have shown how the nutrient can affect sleep “indirectly” through non-specific pain disorders, correlated with alterations in sleep quality, such as restless legs syndrome and obstructive sleep apnea syndrome.

The relationship between vitamin D and melatonin:

It may also has a hand in the production of melatonin, the hormone that signals when it’s time to sleep. When it binds to these receptors, it can influence the synthesis and release of melatonin, thereby affecting our sleep patterns.

“Vitamin D and melatonin are closely interlinked in the regulation of circadian rhythms. Disrupted melatonin rhythms associated with vitamin D deficiency have been implicated in impaired sleep onset and maintenance.” Says Dr Bruni.

While melatonin is the primary hormone which governs our sleep-wake cycles, vitamin D indirectly supports its production by controlling tryptophan availability and its conversion into serotonin and ultimately melatonin.

Deficiency and sleep disorders:

Dr. Bruni says, “Among various sleep disorders, insomnia, restless legs syndrome, and obstructive sleep apnea have shown the most consistent associations with vitamin D deficiency.”

Also playing an important role in both serotonergic and dopaminergic systems by regulating gene production and transcription.

“These mechanisms are particularly relevant to insomnia, where serotonergic dysregulation is implicated in poor sleep quality and reduced REM sleep, and to restless legs syndrome, where dopaminergic dysfunction plays a central pathophysiological role,” says Dr. Bruni.

While being one of the most important nutrients for our health, it’s also one that most of us don’t get enough of. In the UK, nearly half (49.5%) of adults have below-optimal levels of the nutrient.

For those looking to increase their Vitamin D levels, consider these practical tips: