An apo-E increase had not yet been noted in other DHA studies with humans. For three months, about a teaspoon of DHA- rich oil was added to salad dressings or bean, salsa or guacamole dips served to six volunteers, substituting safflower oil in the servings for the four other men. Both occur in fish oils thought to have cardiovascular benefits. The vitamin is essential for absorbing calcium and thus integral to strong bones. The African-Americans also had smaller increases in circulating vitamin D during summer.
Sunlight stimulates skin to make the vitamin, but pigmented skin makes less.
What's more, in the winter when vitamin D levels are lowest, an important hormone called parathyroid hormone was elevated only in the African- American women. This hormone signals low blood calcium and can stimulate loss of calcium from the bones. Apparently, African-American women living in northern latitudes don't manufacture enough vitamin D during the summer to carry them through the winter months, the researchers concluded. The amounts of vitamin D and calcium in the diets of the two groups of women did not differ enough to explain the differences in their blood levels of the vitamin.