I really think that eating well is critical for the absorption of vitamin and other useful nutrients . For example, If one is deficient of healthy saturated fat (eg: Good saturated fat found in pastured meat or coconut/tropical oil )by eating bunch of junk food loaded with sugar and trans fats (except CLA), I believe he/she is also likely to be deficient in fat soluble vitamins and essential fats such as omega fatty acids even with supplementation (eg: fish oil).
saturated fatty acids enhance the absorption and metabolism of omega-3 fatty acids through the delta-6-desaturase (D6D) pathway