Vitamin D Supplementation

"Numerous studies within the last twenty years have linked vitamin D deficiency or insufficiency to various types of cancer, Alzheimer's disease, Type 2 diabetes, heart disease, pregnancy complications and more."
Dan NEwton, molecular biologist, research scientist, Medical University of South Carolina

"We are starting to see some studies show that vitamin D doesn't have a benefit, even for bone health. However, these studies are in people who have generally good vitamin D blood levels."
"It's not surprising that giving them more of a nutrient they already have enough of doesn't lead to better health outcomes."
James Fleet, professor, nutrition science, Purdue University

"Overall, the clinical trial research has shown that there are some benefits of vitamin D supplementation, but they are more limited than what was originally proposed."
"A few years ago, people believed that vitamin D was a panacea that could prevent every major chronic disease."
"This may be [why the VITAL trial failed to link vitamin D supplementation to a reduction in heart disease or stroke risk] because the amount of vitamin D needed for heart health is relatively modest to moderate, similar to the amount needed for bone health and already achieved by many without taking supplements. For cancer reduction, there may be benefits with larger doses."
"We found a strongly significant reduction in cancer death of 13 percent across the five trials, which included VITAL."
JoAnn Manson, chief, division of preventive medicine at Brigham and Women's Hospital, Harvard Medical School professor, lead author, VITAL study

According to a 2015 report published in the Journal of the American Medical Association, 2012 saw a fourfold increase in vitamin D supplementation by American adults as compared to a decade earlier. This, in recognition of the generally low dietary intake of vitamin D linked to studies widely publicized during that time suggesting its intake could prevent a large and varied types of chronic diseases.

More latterly, uncertainty relating to vitamin D's usefulness based on two recently published studies, has arisen; the first a meta-analysis published in The Lancet Diabetes & Endocrinology, suggesting that vitamin D supplemental intake has not been seen to reduce the risk of falls and fractures, nor has it be understood to have led to clinically significant improvement in bone mineral density.

The Vitamin D and Omega-3 Trial, also referred to as VITAL, represents the second study which focused on whether taking 2,000 international units (IU) of vitamin D daily for men over 40 and women over 55 might prevent cancer and cardiovascular disease over five years. This was a randomized control trial of over 25,000 American participants.

The finding of the report was that "supplementation with vitamin D did not result in a lower incidence of invasive cancer or cardiovascular events than did a placebo". Vitamin D is required for absorption of calcium and phosphorus into bones and teeth, which made it a recognized hormone promoted for its bone health facilitation -- since with a lack of sufficient vitamin D, calcium leaches from bones, resulting in loss of bone strength which can in turn lead to rickets in children and osteomalacia (softening of the bones) or osteoporosis in mature people.

In the Lancet study, only six percent of the 81 trials the analysis depended upon for its conclusion represented people with vitamin D deficiency. The conclusion in view of this fact represents an oversimplification of the trial results. Dr. Manson points out that the reasons her VITAL trial failed to link vitamin D supplementation clearly to a reduction heart disease or stroke risk may be attributable to many causes. She and her colleagues published a meta-analysis of vitamin D supplements linked to health outcomes in the Annals of Oncology. In the studies they interpreted, the dosages of vitamin D went from 833 to 2,000 IU daily.

Cancer develops over several decades, and many of the studies had fewer than five years of followup, pointed out Dr. Manson. It was therefore not to be expected that their study demonstrated that the development of cancer was not statistically at variance for the vitamin D group, versus the control group in their meta-analysis.  The recommended amount of vitamin D from diet and supplements based on bone health search has yet to be set by the National Academy of Medicine.

Should anyone consume three ounces of salmon twice weekly, have a cup of milk and two eggs daily, that would amount to 330 IU of vitamin D each day. Whereas the current recommendations are 400 IU of vitamin D for infants, 600 IU for men and women ages one to 70 years, and 800 IU for adults 71 or older. The human body can synthesize vitamin D with exposure to sun, but the Dietary Reference Intakes for vitamin D make the assumption that most people limit their direct exposure to the sun.

Aside from the fact that sun exposure is mostly seasonal, most people spend most of their time indoors; many people live at northern latitudes and see less sun in their daily lives; and those that do experience frequent sun exposure, most likely use sun protection lotions or clothing cover-ups to reduce skin cancer risks.