There have been many studies on vitamins such as A, E, and C which show very little benefit and even some increased harm in the case of vitamin E when taken as a supplement. Of course we need these vitamins in the food we eat, but some nutritionist comment that if you are paying a lot for a daily vitamin, you are just creating expensive urine. However, when pressed, these nutritionists usually will say, If you are taking a daily vitamin, keep it up.
There are several exceptions to this pessimistic view on vitamin supplementation. One is fluoride for children while their teeth are developing. Another is folate for all women of child-baring age who could possibly get pregnant. Folate supplementation has proven to decrease the rate of spina bifita, neural tube defects, and anencephaly in newborns. The reason you need to take it before you are pregnant is because by the time you know you are pregnant, the benefit of taking folate is gone. The important stuff is already done. Now, the focus and attention has turned to vitamin D.
It turns out that Vitamin D is not just a vitamin but also a hormone. Vitamin D is produced in the skin upon exposure to UV light. Vitamin D then must be converted into its active form by traveling to the lungs and kidneys, becoming 1,25-dihydroxycalciferol. Thats the good stuff. However, people with kidney or lung disease may not be able to convert calciferol into the active form and may be deficient.
It has been assumed for decades that all that Vit D was good for was bone formation. It turns out that Vit D does way more that that. Some of which we are only now discovering. Now we are discovering that Vit D is way important for the development of fetal brains and future IQ, as well as brain health and volume throughout life. Scientists have found that seniors with significant brain atrophy and Alzheimer's have low vitamin D levels. Genes linked with the development of Alzheimer's disease are associates with how the brain metabolizes Vit D.
Also, science is finding out that there is a link between Vitamin D and autoimmune disease. Patients who receive high does of Vit D supplementation have significantly less MS relapses. Also, patients with Inflammatory Bowel Disease have less symptoms after taking Vit D. Vitamin D is also being said to prevent Rheumatoid arthritis.
Doctors have known for decades that the bone disease called rickets is the consequence of low Vit D. The issue here is that when doctors set normal values for Vit D levels, the levels were set based on the point at which rickets and osteoporosis set in. But, at that time, doctors didn't know that the vitamin served so many other purposes for the immune system as well as the brain. The consequence of this is that even if your have had your Vit D level checked and it came back normal, it may not be normal if its low normal.
As far as MS is concerned. This is a disease that people only get in the higher latitudes. No one in the tropics gets MS. So, we have known all along that this probably had something to do with the sun. In fact, African Americans who never get MS, are at increased risk to contract MS if they move to nothern latitudes. The leading theory is that there is a gene that has been identified on Chrom 6 which is influenced by Vit D while the fetus in in the womb. the children of women with this gene mutations and who have mothers with low sun exposure and low vit D levels are at much greater risk of developing MS.
But before all pregnant women get out in the sun, UV light isn't all good. Too much UV light destroys folate. And low folate causes those terrible spina bifita defects. Vit D has been in our milk by as we get older we tend to become lactose intolerant and therefore stop drinking it. Another issue is the color of our skin. People in northern latitudes developed lighter skin so that they can produce more Vit D. But the trade off is less folate. People with darker skin actually have a more difficult time producing vit D because the high melanin in their skin absorbs the UV light before it can reach the cells that make Vit D. This especially becomes even more of an issue for people with dark skin who live at the equator who then move to extreme northern or southern latitudes.
When it comes to preventing osteoporosis, I would add that getting vit D is much more important than taking Calcium. There is usually plenty of calcium around, but its the vit D that is the problem. If you are going to take a calcium supplement, be aware that most calcium is not absorbed well at all. Citrical is a formulation that is absorbed better than typical Calcium salts like in Tums. Ester-C wasn't that much better than Tums.