Nutritional testing of circulating levels of fat-soluble vitamins (FSV) provides a good indication of their status throughout the body. All FSV have vital independent physiological functions, but there are also very important interactive functions among the FSV that should be considered. Beta-carotene, an anti-oxidant and excellent indicator of fruit and vegetable consumption, is the primary plant source (precursor) of vitamin A (retinol). Beta-carotene has other functions and its conversion to vitamin A varies significantly among individuals. Low thyroid function may slow the conversion of beta-carotene to vitamin A, and a significant percentage of the female population has diminished capacity to convert beta-carotene to vitamin A. The levels of beta-carotene and vitamin A are regulated independently, emphasizing the importance for assessing the status of both vitamin A “vitamers” through nutritional testing.
Vitamin E and CoQ10 are the primary anti-oxidants among the FSV and they protect against oxidation of polyunsaturated fatty acids in cell membranes and circulating lipoproteins; oxidized LDL is an independent risk factor for cardiovascular disease. Among the E vitamers, α- and ᵧ-tocopherol have complementary roles as anti-oxidants with ᵧ-tocopherol having a greater role in protection against reactive nitrogen species. Overconsumption/supplementation with α-tocopherol lowers ᵧ-tocopherol status, emphasizing the need to assess the levels of both primary forms of tocopherol. One also needs to pay attention to very high levels of vitamin E as they may prolong clotting time. That is especially important with poor vitamin K status (elevated undercarboxylated osteocalcin) that may impair with the normal coagulation cascade.
Due to the heightened awareness of the vital regulatory roles of vitamin D, coupled with a high prevalence of vitamin D insufficiency in North America, there has been a significant increase of vitamin D supplementation. Indeed low vitamin D levels have been associated with increased risk of hip fractures, depression, and cardiovascular disease. However, addressing vitamin D status without attention to that of vitamins K and A may be consequential in the long run regarding bone health and undesirable calcium deposition. Vitamin K-dependent calcification of specific proteins, such as osteocalcin, is very important for several physiological functions including and bone and vascular health. A high serum level of undercarboxylated osteocalcin indicates a functional deficiency of vitamin K in the body, and should be addressed along with clinical intervention to optimize vitamin D levels.