- **Vitamin B1 (Thiamine)**: Deficiency can be caused by insufficient levels of vitamin B1 in the body due to low intake in diet or impaired uptake in the gastrointestinal tract. Risk factors include alcoholism, pregnant women, diuretic use, and dialysis.

- **Vitamin B2 (Riboflavin)**: Deficiency can occur due to conditions that prevent your body from absorbing nutrients from food, such as liver disorders. It can also be caused by a lack of these vitamins in your diet.

- **Vitamin B3 (Niacin)**: Deficiency can be caused by a diet low in tryptophans or a condition that reduces the body’s ability to convert tryptophan to niacin, such as Hartnup disease or carcinoid syndrome. Other causes include undernutrition due to alcohol use disorder, anorexia, and inflammatory bowel disease.

- **Vitamin B5 (Pantothenic Acid)**: Deficiency can occur due to certain medications, long-term dieting, biotinidase deficiency, and other genetic causes. Certain stomach conditions or operations can also prevent the absorption of enough vitamin B5.

- **Vitamin B6**: Deficiency can occur in people with kidney disease or conditions that prevent the small intestine from absorbing nutrients from foods. Certain autoimmune disorders, some epilepsy medications, and alcohol dependence can also lead to vitamin B6 deficiency.

- **Vitamin B7 (Biotin)**: Deficiency can be caused by certain medications or conditions that prevent the small intestine from absorbing nutrients from foods. Other factors include being on parenteral nutrition for long periods, taking anti-seizure medication over a long period, which can lower the body’s biotin levels.

- **Vitamin B9 (Folate)**: Deficiency can occur due to a lack of these vitamins in your diet, certain medicines, including anticonvulsants and proton pump inhibitors (PPIs), which can affect how much of these vitamins your body absorbs. Conditions that affect your intestines can also stop you absorbing the necessary amount of vitamin B9.

- **Vitamin B12**: Deficiency can occur due to pernicious anaemia, where your immune system attacks healthy cells in your stomach, preventing your body from absorbing vitamin B12 from the food you eat. A lack of these vitamins in your diet, certain medicines, including anticonvulsants and proton pump inhibitors (PPIs), can affect how much of these vitamins your body absorbs.

Please note that this information is general in nature, and individual health concerns may vary. It's always a good idea to consult with a healthcare provider for personalized advice.