Vitamin D3 is a rampant deficiency in sun-phobic men and women; the further north you live (above the equator), the more likely to be deficient. Levels below 30 ng/dl cripple the immune system. Optimum number keeps going up; shoot for 70 ng/dl. That takes 5000 IU – 10000 IU/day in winter. Get yourself tested (25-OH-vitamin D test) and supplement accordingly. Most cells in the body have vitamin D receptors, so it is probably more important than we actually know.
Secondly, vitamin D is not activated for bone formation without vitamin K2, so I suggest using a form of D3 that comes with K2, like Life Extension’s D+K+I (I like the Iodine for health of most secretory glands as well, unless you have an allergy to it).
Finally, vitamin D doesn’t work well without adequate Magnesium, which is another rampant deficiency in today’s populations, because our soils have around a quarter of what was in them 150 years ago (in the USA). I sleep better taking mine with dinner; I use Magnesium Malate because it will not give me the runs, and the body needs malic acid as well; works to relax me for the evening, and prevents most forms of muscle cramping.
So there you have a powerful combination of nutrients that tune up your body to thrive into advanced age with greater strength of bone and muscle, an immune system that will prevent most of the diseases of aging and keep you independent for a decade or so longer than most of your friends.
To your Greater Health and Fitness,
And if you live near Simi Valley CA, let me show you all my strategies for staying fit and strong into advanced age at Fitness 19; two half-hour sessions a week is all I need to put you on the path to Senior Fitness