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The Lab Tests Online website is developed in collaboration with other laboratory professional societies and is funded in part through corporate sponsorships. Please click to see a complete list of the site's collaborating partners or corporate sponsors.B12 and Restless Leg Syndrome 1 What is Vitamin B12? 2 Restless Leg Syndrome and Vitamin B12 2.1 What is Restless Leg Syndrome? 2.2 How Vitamin B12 Deficiency May Cause Restless Leg Syndrome 2.3 How to Take Vitamin B12 for Restless Leg Syndrome Vitamin B12 is also called cobalamin. This water-soluble B vitamin is involved in a number of cellular processes including metabolism, DNA synthesis and energy production. Vitamin B12 is the most complex vitamin and it is the only one to contain a rare element (cobalt). There are 4 known forms of vitamin B12. First, there is cyanocobalamin which is the form contained in most vitamin B12 supplements. It is produced from hydroxycobalamin, the form of the vitamin produced by bacteria.
During the process of purifying hydroxycobalamin with activated charcoal, it picks up cyanide to form cyanocobalamin. The second form of vitamin B12 is hydroxocobalamin which also produced by bacteria. The other two forms of vitamin B12 are methylcobalamin and adenosylcobalamin. These are the forms of the vitamin produced in humans. Dietary sources of vitamin B12 include plants and animals that have native bacteria producing the vitamin. Plants are not excellent sources of vitamin B12 since those bacteria are found in soils or roots and most of the vitamin B12 content are washed off before or during cooking. Animal liver is an especially excellent source of vitamin B12. Other animal sources of the vitamin are fish, shellfish, egg, milk, milk products and poultry. Vitamin B12 is also sometimes added to food and drink products especially energy drinks. They are also available as supplements in different dosage forms. The recommended daily intake of vitamin B12 is 2 – 3 micrograms per day.
Vitamin B12 deficiency can cause extensive damage to the brain and central nervous system. Even mild deficiency of vitamin B12 causes depression, tiredness and poor memory. More extensive and permanent damage to the brain are caused by chronic vitamin B12 deficiency. Vitamin B12 deficiency is mostly caused by pernicious anemia. Since anemia is also linked with iron deficiency (through the loss of heme iron from the body), this vitamin is indirectly linked to disorders caused by iron deficiency such as restless leg syndrome. Restless leg syndrome produces some odd sensations in the limbs. These sensations can be painful or not; they can occur as ache, itch or tickle, and moving the affected limb provides some measure of relief. Since vitamin B12 deficiency can damage nerves in the central nervous system, some have attributed these odd sensations to the effects of vitamin B12 deficiency on the nerves. However, restless leg syndrome can present even without these odd sensations.
There are defining characteristics of this neurological disorder. It is primarily described as an irresistible urge to move the limbs. The restlessness usually worsens with prolonged rest and especially during the night. It is also relieved temporarily by moving the restless limb. Restless leg syndrome may be caused by an underlying disease/disorder or certain drugs. Vitamin B12 deficiency falls under the first group along with iron and folate deficiencies. The syndrome is also linked to autoimmune diseases such as celiac disease and rheumatoid arthritis as well as neurodegenerative diseases such as Parkinson’s disease and peripheral neuropathy. Given the importance of vitamin B12 in cellular metabolism, DNA synthesis and control as well as in protection of the nervous system, its deficiency can as well contribute to these autoimmune and neurodegenerative diseases. Lastly, restless leg syndrome has a strong genetic component. It is estimated that 60% of people living with this disorder inherit it.
Different genes and chromosomal loci have been identified in different races to be associated with increased risk of restless leg syndrome. Vitamin B12 deficiency may contribute to restless leg syndrome in 2 ways. First, this deficiency can cause significant damage in the central nervous system including in the brain. It is quite possible that such damage can occur on the parts of the brain regulating motor functions. Since restless leg syndrome is essentially caused by improper coordination, control and inhibition of excessive movement, damage to the neurons responsible for these functions may cause symptoms resembling restless leg symptoms. Such damage do not have to be cell deaths in the brain. It may well be that vitamin B12 deficiency leads to the production of dysfunctional enzymes and surface proteins such as the ones known to prevent the absorption of iron into the cells of the substantia nigra. Low iron level in the cerebrospinal fluid is one of the major diagnostic signs of restless leg syndrome.
Iron is needed to produce dopamine which is the chief neurotransmitter for regulating the coordination of fine motor function such as limb movements. Since vitamin B12 is closely linked to iron levels in the body, the vitamin deficiency is often seen along with iron deficiency. Anemia causes both the loss of iron and vitamin B12. Therefore, where anemia is the cause of restless leg syndrome, vitamin B12 supplementation is especially important for treating the anemia, preventing further iron loss and overcoming the deficiencies that cause restless leg syndrome. Vitamin B12 deficiency is only a secondary cause of restless leg syndrome. In fact, it has not been directly linked with the syndrome even though there are a few recorded cases of patients with this deficiency. However, given the increased incidence of iron deficiency and the strong association between both deficiencies, vitamin B12 does not feature prominently in the research and treatment of restless leg syndrome.
Of the few papers written on the topic, the 1993 study published in the Journal of Postgraduate Medicine stands out. This study accessed the prevalence of restless leg syndrome among elderly patients and noted both iron and vitamin B12 deficiencies as common and treatable causes of the syndrome. In fact, in the few patients where marked vitamin B12 deficiency was known to cause restless leg syndrome, a complete resolution of symptoms was observed 1 month after starting on vitamin B12 supplementation. Up to 1000 micrograms per day is recommended to correct severe vitamin B12 deficiency before reducing the dose to 2.5 micrograms per day. However, such severe deficiency would need hospitalization in the first place. Vitamin B12 supplements are available in different dosage forms including oral, sublingual, nasal spray and injectable forms. Absorption following oral intake of vitamin B12 is low, therefore, the strength of the vitamin taken far exceeds the recommended daily intake.