Many medicines can impair the body’s supply of water-soluble vitamins, especially B-vitamins. Hence, a folic acid deficiency can result from taking the antiepileptic drug phenytoin, as it accelerates the folic acid metabolism while simultaneously inhibiting the folic acid uptake. This can lead to raised homocysteine levels in the blood, an overgrowth of the gums (gingival hyperplasia) and a drop in biotin levels (18, 19). Pregnant epileptic women demonstrate an increased risk of giving birth to a child with defects due to folic acid deficiency (e.g., neural tube defects) and should therefore take folic acid if possible before conception as a preventive measure (20,21). Methotrexate, an antirheumatic drug used to treat rheumatoid arthritis (RA), the most common form of inflammatory arthritis, can also negatively influence folic acid concentrations. Osteoarthritis is the most common disease on the planet. Around 1% of the world’s population suffers from deterioration of the joints and their extremely painful, inflammatory form, RA. Methotrexate is a folic acid antagonist that inhibits key enzymes in folic acid metabolism and can therefore induce folic acid deficits (22).
Diuretics, which support the elimination of water and electrolytes via the kidneys, have a broad range of therapeutic actions and are thus primarily used for treating many widespread diseases, such as heart failure, hypertension and edemas (23,24). Diuretics, especially the loop diuretic furosemide and the potassium-sparing diuretic hydrochlorothiazide/triamterene, cause an increase in the elimination of water-soluble vitamins like B6, B12 and folic acid and lead to insufficiencies in the body. Triamterene can also reduce the uptake of folic acid and its bioavailability (25).
A fall in blood folic acid levels and a rise in homocysteine concentrations can also be caused by constipation medication. Patients suffering from chronic constipation, which affects up to 20% of the adult population, regularly use laxatives that accelerate intestinal voiding. Some, like bisacodyl and sodium picosulfate, inhibit the uptake of sodium and water from the intestine, causing an influx of electrolytes and water-soluble vitamins into the intestine and increasing their rate of excretion (26).
Diabetes mellitus is a common chronic disorder of blood sugar metabolism, which is associated with a significant risk of severe complications and sequelae in the cardiovascular and nervous systems (27,28). The most common form is type 2 diabetes, in which the cells of the body do not utilize insulin efficiently. Treatment often includes substances to improve the organism’s sensitivity to insulin. However, the oral antidiabetic drug metformin hydrochloride, for example, concomitantly lowers blood levels of vitamin B12 and folic acid by reducing their uptake from the gastrointestinal tract, which can exacerbate nervous disorders (neuropathies), like tingling and numbness, especially in the hands and feet of those affected (29,30).
Among the most frequently prescribed drugs in the world are proton pump inhibitors (PPI). These are substances that suppress the production of gastric acid with the aim of preventing gastric ulcers. But PPI not only prevent the production of gastric acid, they also prevent the release and utilization of vitamin B12 from food. And a vitamin B12 deficiency can increase the risk of cognitive disorders and decrease mental capacity, particularly in older patients (31,32,33).
Proton pump inhibitors also reduce the bioavailability of dietary vitamin C (32,34). A further potential disruptive factor to vitamin C status is the painkiller (analgesic) acetylsalicylic acid (ASA): the most frequently used medication with pain-relieving and anti-inflammatory properties worldwide. The mucous membrane of the stomach contains high concentrations of vitamin C. However, ASA can disturb the gastrointestinal vitamin C balance, thus leading to a fall in tissue levels of the vitamin. In addition, a reduction in blood plasma concentrations of vitamin C and an increased elimination of the vitamin in urine have been observed (35,36). Furthermore, studies have found a link between ASA administration and vitamin B12 deficiency (37).
An estimated 235 million children and adults around the world suffer from asthma and the most common children’s afflictions worldwide are bronchial diseases (38). Besides corticosteroids, the active substance theophylline is also used for the treatment of asthma. This substance inhibits the activation of vitamin B6 and can thus lead to a fall in blood vitamin B6 concentrations and a rise in homocysteine levels (39).