I have started with D3 supplementation, and had bi-polar moodswing issues until I learned about the magnesium connection. When I did 20,000 iu D3 I had -excellent- mineral absorbition, and was doing magnesium at the same time. It became -too- much absorbition, and I had a bout with hypercalcemia.
Basically the best thing to do is to get ahold of boron, k2, and combine that withyour magnesium and D3. It's available in a combined product called 'D3-plus' from biotech labs, though the mix is a little pricey.
Boron helps keep the magnesium in your body instead of being stripped by your kidneys. It's very rich in almonds, and decently high in apples, so almonds are definately the way to go.
Natto (japanese fermented soybeans) is the food highest in K2 - k2 is otherwise released in very small amounts by the digestion of probiotics in the gut. It can be one of the big reasons that the immune system functions so much better for folk on probiotics- k2 pushes calcium to the organs that need it, such as the bones and endocrine system, and with higher mineralization, the body likely has an easier time producing antibodies.
I have found that combining magnesium with a b-complex vitamin helps reduce the sleepiness, and ups mental acuity a little. In french magnesium supplement products they combine magnesium with it's helpers, b-complex, selenium and a little E. Basically almost all foods that contain high magnesium contain some variety of B-complex.
How can I illustrate? Well, natural foods are much more balanced in nutrition than actual supplements. A diet high in the right foods should help absorbtion a great deal, but D3 is a maaaajor factor in allowing you to absorb the nutrients you need.
When I took B-complex without magnesium, my blood glucose levels would stay high for hours. When I took magnesium without b-complex, my head would get that spacey feeling, especially when my blood Sugar would go low.
I can reccommend no better food than pumkin seeds, sunflower seeds, or sesame seeds to help you absorb b-complex, omega-fatty acids, and magnesium together. I highly reccommend having some fun making yourself a trail mix at the store of: Almonds, macadamia nuts, organic raisins and cranberries (dried blueberries if you can get them), sunflower and pumkin seeds, and if you feel like it, dried banana chips or apple chips. It's important to watch out that the carb percentage on them isn't too high, but it's a delicious way to do yourself good.
If you want to get the maximum effect out of multivitamins, then you might want to try chlorella or spirulina -instead of- a pharmeceutical multivit. Multivitamins are actually hard for the body to absorb because they are synthetically produced- the producers even have to wrap the pills in a protien-powder from shellac/insect origin to keep the powders from irritating the digestive track. They are also sadly lacking in amino acids, which are some of the major building blocks of hormones, neurotransmitters and tissues in the body.
Spirulina and Chlorella are basically algae. They are used as a high-nutrient fish food, and under laborator analysis, they are very high in the essential building blocks of life - even the b-complex vitamins, and many minerals.