In the past few years, there has been a recognition that there is a widespread deficiency of Vitamin D in many adults. While Vitamin D is associated most often with healthy bones and teeth, this nutrient is wide-ranging in its benefits for health in every organ system in the body (e.g. cardiovascular health, cancer prevention etc.). The evidence for the almost panacea benefits of Vitamin D is present in population studies of nutritional profiles, but an increasing number of basic science observations confirm its potent and versatile benefits on health.
There seems to be no doubt that average intakes of Vitamin D are inadequate in most diets. Strong arguments have emerged that inadequate exposure to sunlight impairs the body’s ability to synthesize Vitamin D, but excessive sunlight exposure is not considered healthy because of risks of skin cancer and skin photo-aging. Advice on the ideal amount of Vitamin D supplementation of the average adult diet is wide-ranging to a degree that has caused confusion among healthcare givers and consumers.
To overcome this problem, medical practitioners have advised the assessment of Vitamin D status by direct measurement of serum levels of 25-hydroxylation of Vitamin D (25, OH, D). The hydroxylation of Vitamin D takes place in the liver to a major degree, but other tissues can convert to this active form of Vitamin D (25, OH, D) e.g. testes and ovaries. There are differences of opinion on the interpretation of blood levels of 25. OH, D, but many nutritionists attempt to place the level in serum to 90-100 nmol/L. This perceived optimum serum level is inferred from nutritional studies in various populations (as mentioned earlier) and this continues to create debate among scientists on what ideal blood levels of Vitamin D should be. Scientists with an interest in hormone replacement therapy stress the importance of Vitamin D in balancing sex hormones e.g. testosterone and DHEA and adequate intake of this vitamin is considered to be particularly important in hormone balancing (in simplistic terms).
How much Vitamin D is safe in daily supplements? There is no precise answer to this question for several reasons. The existing Vitamin D status of the individual, diet, their exposure to sunlight and other factors determine dosage requirements. Vitamin D toxicity is a real issue even though it may be uncommon. These circumstances add up to several guidelines for the safe and effective use of Vitamin D supplements.
• Current and even some revised upward recommendations for Vitamin D are often inadequate (e.g. 400 or 800 IU per day) but this is still a matter of debate.
• Vitamin D status should be checked by measuring 25, OH, D serum levels and monitored when large dosages of Vitamin D are used.
• The best form of Vitamin D for supplementation is Vitamin D3.
• Products with very high doses of Vitamin D (tens of thousands of units cannot be considered safe).
• The safety of taking more than 2000 IU of Vitamin D daily must be questioned without strict medical supervision.
• The nutritional benefits or effectiveness of very large doses of Vitamin D remain in question. Many physicians feel comfortable with a regular daily intake of 1000 IU of Vitamin D, but major deficiencies of Vitamin D may require a limited period of high dosage therapy, under medical supervision.
Note: There is considerable debate optimal Vitamin D intake and its importance in disease prevention. Until clarity of the safety and effectiveness of high dosage Vitamin D supplementation becomes clear a certain degree of caution is required.