Muscle weakness can be a frightening thing to experience and can have many causes. One potential cause of muscle weakness is vitamin deficiency, particularly of some of the B vitamins, but because treatment of relies on identifying the underlying cause, you should see your doctor if you are experiencing muscle weakness.
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About the B Vitamins
According to Medline Plus, the B vitamins are a group of eight vitamins that your body uses for energy metabolism and red blood cell production. They include thiamin, or B-1; riboflavin, or B-2; niacin, or B-3; pantothenic acid, or B-5; pyroxidine, or B-6; biotin, or B-7; cobalamin, or B-12; and folate. B vitamins are found in a variety of plant- and animal-based foods, with the exception of B-12, which is primarily found in animal-derived products.
Weakness is a symptom of many diseases. For example, according to Richard LeBlond and colleagues in "DeGowin's Diagnostic Evaluation," diseases of the brain and spinal cord, the peripheral nerves, or of muscles can cause weakness, as can generalized metabolic disturbances or systemic diseases such as cancer or viral infection. Determining what brings on your weakness can help you figure out its cause. For example, weakness when climbing stairs suggests that you have a disease affecting your upper legs.
Vitamin B-1 Deficiency
According to Medline Plus, thiamine deficiency is most often seen in alcoholics, both because severe alcoholics tend to be malnourished and because alcohol makes it harder for your body to absorb thiamine from the diet. Besides weakness, symptoms of thiamine deficiency include fatigue and nerve damage. A particularly severe complication of thiamine deficiency is Wernicke-Korsakoff syndrome, a combination of incoordination, confusion and memory disturbance.
Vitamin B-12 Deficiency
According to the Office of Dietary Supplements, vitamin B-12 deficiency is most commonly seen in people with gastrointestinal diseases that impair normal nutrient absorption, such as Crohn's disease and pernicious anemia. B-12 deficiency also can occur in vegetarians or vegans who do not take B-12 supplements. Along with weakness, other symptoms of B-12 deficiency include anemia, incoordination, and numbness and tingling in the hands and feet.
Other Causes of Weakness
One example of a non-vitamin-related cause of weakness is Guillan-Barre syndrome, an autoimmune disease that causes lower-extremity weakness after viral infections, most commonly of the gastrointestinal tract or lungs. According to Stephen L. Hauser and Arthur K. Asbury in "Harrison's Principles of Internal Medicine," with prompt treatment approximately 85 percent of people experience full recovery from Guillan-Barre. However, mortality from this condition can be as high as 5 percent, and even those people who recover might have recurring symptoms later.