Iron and sleep quality – does a deficiency affect recovery?

Sleep quality can be disrupted not only by taking too long to fall asleep. The problem is not just tossing and turning restlessly, but also falling asleep almost immediately after getting into bed, when it feels more like passing out from exhaustion than drifting peacefully off to sleep. If you feel tired in the morning despite a full night’s sleep, it is worth looking not only at the length of your sleep but also at factors affecting the nervous system and energy metabolism. One of these may be iron.

1. Sleep and recovery
2. Iron and the nervous system
3. Diet and iron

Sleep and recovery

Sleep is closely linked to the functioning of the nervous system, as during sleep there are changes in brain activity, muscle tone, response to stimuli, the rhythm of hormone secretion, and the balance between arousal and relaxation in the body. Put simply, falling asleep requires a gradual shift of the nervous system from wakefulness towards a greater dominance of calming mechanisms.

Neurotransmitters – substances that transmit signals between nerve cells, such as gamma-aminobutyric acid, serotonin, dopamine, acetylcholine, noradrenaline and histamine – play a significant role here. Their activity varies depending on the time of day and the sleep phase. The brain functions differently during deep sleep than during REM sleep (rapid eye movement), during which dreams occur and there is increased activity in specific areas of the brain.

Sleep is also linked to the body’s circadian rhythm, which regulates the onset of sleepiness, body temperature, melatonin secretion and the morning increase in stress axis activity. For this reason, sleep quality can deteriorate not only when rest time is too short, but also due to irregular bedtimes, exposure to light in the evening, chronic mental stress, pain, intense physical exertion late in the evening, or an insufficient energy intake in the diet.

"During deep sleep phases, the body enters a recovery mode. During this time, the secretion of growth hormone increases, which plays a role in tissue repair and exercise adaptation. At the same time, levels of cortisol – a stress-related hormone – decrease, allowing the body to switch from an active mode to a recovery mode." Łukasz Domeracki – Dietitian

Iron and the nervous system

Iron is important for the nervous system not only because it plays a role in oxygen transport, but also because it is involved in the processes necessary for the proper functioning of nerve cells. The brain has high energy requirements, which is why it is sensitive to disruptions in oxygen supply and to limitations in cellular metabolism. This element is also discussed in the context of the synthesis and metabolism of selected neurotransmitters, which are important for the control of movement, motivation, wakefulness and certain aspects of sleep regulation. Consequently, it has been studied, among other things, in restless legs syndrome.

Symptoms of iron deficiency, such as fatigue, weakness, drowsiness, impaired concentration, reduced performance and increased tiredness, may partially overlap with the symptoms of sleep deprivation. However, caution is required in diagnosis, as such symptoms are non-specific and may also result from sleep deprivation, stress, low energy intake, vitamin B12 deficiency, thyroid disorders, infections, inflammation or training overload.

Estimated iron content per typical serving of selected foods

Diet and iron

According to the nutritional guidelines for the Polish population, the recommended daily intake of iron is 10 mg for adult men, 18 mg for women aged 19–50, 10 mg for women over 50, 27 mg during pregnancy and 10 mg during breastfeeding. In food, iron occurs as haem iron, found in animal products, and non-haem iron, typical of plant-based products. Its sources include meat, offal, fish, eggs, pulses, pumpkin seeds, nuts, buckwheat and whole grains. The iron content in this group of products can vary roughly from around 1 mg/100 g in some fish and eggs to over 10 mg/100 g in selected offal, seeds and nuts.

The absorption of non-haem iron can be enhanced by vitamin C, whilst it can be reduced by phytates, polyphenols, calcium, and coffee and tea consumed immediately with a meal. Iron supplements are usually available in capsules, tablets, drops or liquids, and their use should be tailored to one’s diet, test results and individual requirements, as iron should not be taken "in reserve".

Джерела:

• Avni, T., Reich, S., Lev, N., & Gafter-Gvili, A. (2019). Iron supplementation for restless legs syndrome - A systematic review and meta-analysis. European journal of internal medicine, 63, 34–41. https://doi.org/10.1016/j.ejim.2019.02.009
• Datta, S., & Maclean, R. R. (2007). Neurobiological mechanisms for the regulation of mammalian sleep-wake behavior: reinterpretation of historical evidence and inclusion of contemporary cellular and molecular evidence. Neuroscience and biobehavioral reviews, 31(5), 775–824. https://doi.org/10.1016/j.neubiorev.2007.02.004