The hormone which regulates sleep-wake cycle in man is

Options

A. Oxytocin
B. Vasopressin
C. Thyroxine
D. Melatonin

Answer

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks for the hormone that regulates the sleep-wake cycle in humans.

2. **Review the Options**: The options provided are oxytocin, vasopressin, thyroxine, and melatonin.

3. **Evaluate Each Option**:
- **Oxytocin**: This hormone is primarily involved in childbirth and breastfeeding. It does not play a role in regulating the sleep-wake cycle. Thus, this option is incorrect.
- **Vasopressin (ADH)**: This hormone is responsible for water retention and vasoconstriction. It is not associated with the sleep-wake cycle. Therefore, this option is also incorrect.
- **Thyroxine**: Secreted by the thyroid gland, thyroxine is involved in various bodily functions such as metabolism, heart function, and brain development. However, it does not regulate the sleep-wake cycle, making this option incorrect as well.
- **Melatonin**: This hormone is produced by the pineal gland, especially at night, and is closely linked to the regulation of the sleep-wake cycle. It is known to help in managing sleep patterns and is often used as a supplement for insomnia. Thus, this option is correct.

4. **Conclusion**: The hormone that regulates the sleep-wake cycle in humans is melatonin.

**Final Answer**: Melatonin

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