There are indeed side effects associated with a vitamin B complex. Possible side effects include dizziness, frequent urination, change in the colour of the urine, black stools, constipation, diarrhea, abdominal pain, nausea, vomiting, redness of the skin and itching. Vitamin Bs are best obtained from food sources and they are useful in liver and nervous system functioning and provide us with healthy skin, hair and eyes.
B vitamins affect our metabolism. This would mean that excess vitamins in a B complex supplement may upset our digestive system and cause changes in the consistency and colour of the stools. Yellow stools may also indicate liver problems, one of the side effects of taking too much vitamin B.
If the stools remain a shade of brown, one need not worry about the stool colour. The amount of bile in the stool also affects the colour. If stool passes through our digestive tract quickly, it does not absorb much bile. The stools may turn lighter and become looser. Several B vitamins can cause diarrhea.
Also, excess amounts of vitamin C (ascorbic acid) and vitamin B5 in particular are known to cause diarrhea. There are other supplements that can cause loose stools, such as magnesium and fish oil. Our body cannot digest large doses of either substance.
Another point to take note of is: Persons who underwent gut surgery, or have a history of irritable bowel syndrome, Crohn's disease or other conditions that affect the digestive system, may be more sensitive to vitamin supplements than others.
