Original sentence: Also, people with darker skin have a greater tendency toward vitamin D deficiency when living far from the Equator.Having lighter skin while living near the Equator or having darker skin while living far from the Equator causes the problems discussed below
Edited sentence: As stated above, people with darker skin have a greater tendency toward vitamin D deficiency if malnourished.The darker one's skin is, the more likely one is to suffer from vitamin D deficiency