Q. I have heard that by increasing cell metabolism, one can reduce the melanin production in the body. Is this true? If so, how can we increase cell metabolism?
A. The pigment-derived component of skin color is determined by the production of melanin in special skin cells called melanocytes. Melanin is then distributed to the other predominant skin cell, the keratinocyte, where it is both stored and broken down. An important hormonal influence on melanin production is called melanocyte-stimulating hormone (MSH). This hormone is produced by the pituitary gland (and other cells) and acts on the melanocytes to stimulate melanin production. You might imagine that two things could affect the overall level of melanin in the skin the rate of production and the rate of breakdown.
Interestingly, the difference between fair and dark skin is mostly a manifestation of a lower rate of breakdown in darker skin. However, when any person is exposed to the sun, darkening of the skin (i.e. tanning) is a result of increased production of melanin by the melanocytes. This is actually a protective response, i.e. an attempt to increase the UV resistance of the skin when exposed to damaging sunlight. I do not know of any agent drug substance that can increase the cell metabolism which in turn reduces melanin production.