Genetics plays a huge role in how well you convert the carotenes into retinol. Some people are great at converting beta-carotene in their diet into the retinol form. Others carry genetic variants that significantly impair that conversion.
There are several genes that can influence your absorption, transport, and need for vitamin B12. Some people need higher amounts of B12, and some people thrive on different forms of B12. Take a look at your genetic data to see if you should up your intake of B12.
For some people, stacking caffeine with carbohydrates will raise their blood glucose levels more than just carbs alone. Learn whether you carry this genetic combo and what to do about it.
We all vary in how well we convert the plant-based omega-3 oils into the DHA and EPA that our body needs. Some people are really poor at this conversion and thus should either eat more fish or consider taking a DHA / EPA supplement.