In human nutrition and biochemistry, which vitamin is also historically referred to as vitamin H, especially for its role in healthy skin, hair and metabolism?

Introduction / Context:
Vitamins in the B complex group often have multiple names, including both numerical labels and older letter-based designations. One such vitamin is commonly associated with healthy skin, hair and energy metabolism and was historically called vitamin H. This question checks whether you can correctly match that older name with its modern numeric and chemical name.

Given Data / Assumptions:

• Vitamin H is an older term used in nutrition texts.
• The modern naming system uses B-complex numbers and chemical names.
• The options list vitamin B7, B12, B3 and B5, each with different roles.
• We assume general textbook knowledge of vitamin functions and names.

Concept / Approach:
Vitamin H is another name for biotin, which is now commonly referred to as vitamin B7. The letter H comes from the German words 'Haar' and 'Haut', meaning hair and skin, reflecting biotin role in maintaining healthy hair and skin. Biotin also plays an important part in carbohydrate, fat and protein metabolism as a coenzyme in carboxylation reactions. Vitamin B12 (cobalamin) is associated with red blood cell formation and nervous system function. Vitamin B3 (niacin) is heavily involved in energy metabolism via NAD and NADP coenzymes. Vitamin B5 (pantothenic acid) is part of coenzyme A. None of these other vitamins carry the historical designation vitamin H.

Step-by-Step Solution:
Step 1: Recall that vitamin H is a historical name used mainly in older nutrition literature.Step 2: Connect vitamin H with biotin, known for hair, skin and metabolic roles.Step 3: Recall that in the modern B-complex numbering system, biotin is labelled vitamin B7.Step 4: Check the options and identify vitamin B7 as one of the choices.Step 5: Recognise that the other vitamins B12, B3 and B5 have different names and functions and are not called vitamin H.Step 6: Conclude that vitamin B7 (biotin) is the correct answer.

Verification / Alternative check:
If you consult standard nutrition tables or medical guides, vitamin B7 is consistently identified as biotin, and many sources list vitamin H as an alternative name. Supplement labels targeting hair and nail health often include biotin and sometimes mention vitamin H in their marketing descriptions. In contrast, vitamin B12 is called cobalamin, vitamin B3 is niacin and vitamin B5 is pantothenic acid without any reference to vitamin H. This confirms that vitamin H corresponds specifically to biotin/B7.

Why Other Options Are Wrong:
Vitamin B12 (cobalamin) is important for red blood cell formation and neurological function but is not known as vitamin H. Vitamin B3 (niacin) plays a role in energy metabolism and is sometimes called the antipellagra vitamin, not vitamin H. Vitamin B5 (pantothenic acid) is associated with coenzyme A and is not the vitamin historically named H. These vitamins have distinct identities and functions, so they do not match the description in the question.

Common Pitfalls:
Students can be confused by the multiple naming systems for vitamins or assume that any B vitamin could be called by a letter such as H. Others may mix up vitamin H with vitamin D for skin due to sun exposure. To avoid confusion, remember that biotin specifically carries the old designation vitamin H, while other vitamins have different traditional names or no letter-based names at all.

Final Answer:
Vitamin H is another name for biotin, which is classified as vitamin B7.