Vitamin D is a hot topic in the news these days and it’s also one of the most controversial subjects in medical research. The main debate centers around how much vitamin D3, a natural “nutrient” synthesized by the body in response to sunlight exposure, the average person needs. Governmental guidelines may be advocating for less-than-ideal vitamin D levels by giving a generalized recommendation for supplementation. It really is up to consumers to do the research to see how much vitamin D is really necessary.
Sources of Vitamin D
The most natural method for getting enough Vitamin D is through good ol’ sunshine. While sunshine may be best, those living farther from the equator or those who stay inside all day – especially in the autumn and winter months – will often experience a dramatic drop in vitamin D status. Glass windows, allow light to pass but can act as a barrier to UVB rays, the most beneficial rays for vitamin D synthesis.   This is why supplementation is a must for most people.
What is the Best Amount of Vitamin D3?
When it comes to setting a uniform value for vitamin D, there are a few opinions. The Food and Nutrition Board (FNB) established the now common 400 IU (international units) per day standard; the Institute of Medicine recommends 600 IU per day. These values are said to help blood levels achieve 20 ng/mL and 30 ng/mL, respectively.
Other experts recommend 1,000-1,500 IU per day.  This typically generates a 60 ng/mL blood level. Even then, this may not be enough. An article in Osteoporosis International suggests 2,000-3,000 IUs be taken every day, especially by the elderly. Some cases of vitamin D deficiency may require up to 10,000 IU per day.
In our experience, 5,000 IUs per day seems to accommodate the needs of most people, especially when you're taking a high-quality vitamin D supplement like Suntrex® D3.
Optimal Blood Levels of Vitamin D
With all the research into vitamin D and human health, it’s a wonder so many health organizations continue to disagree on the correct amount of D3 that should be circulating in your blood! On average, most believe a level between 40-80 ng/mL is suitable for most people. 
How Much Vitamin D is Too Much?
Vitamin D toxicity is rare but it can happen if you take extreme doses of vitamin D supplements. The biggest concern with vitamin D toxicity is an accumulation of calcium in your blood. This condition, known as hypercalcemia, can cause poor appetite, nausea, vomiting, weakness, and kidney concerns. Taking 50,000 IU a day of vitamin D for several months has been shown to cause toxicity. This level is many times higher than any recommended allowance. Always talk to your doctor before taking extreme serving sizes beyond what's recommended.
Testing for Vitamin D
How can we know what our Vitamin D status is at any given moment? Blood measurements.  This is the only sure method to assess Vitamin D levels with certainty. The blood marker to check for is called 25(OH)D, short for 25 hydroxyvitamin-D, and it ranges from 0 to 100 ng/mL (most people aim for a number somewhere in the high middle).
Fortunately, as Vitamin D awareness and importance has grown, getting your blood tested is becoming a far more common request and it's not uncommon for insurance to cover it. Based on the research, investigations, and extensive experience of the aforementioned experts in the field, a safe, somewhat general recommendation is to consume between 2,000 IU to 4,000 IU/day (3,000 IU/day avg.) of Vitamin D3 (cholecalciferol). To ensure optimal supplementation, look into getting tested for 25(OH)D.
- Tuchinda C, Srivannaboon S, Lim HW. Photoprotection by window glass, automobile glass, and sunglasses. J Am Acad Dermatol. 2006 May;54(5):845-54.
- Kumaravel Rajakumar, MD, Susan L. Greenspan, MD, [...], and Michael F. Holick, MD, PhD. SOLAR Ultraviolet Radiation AND Vitamin D. Am J Public Health. 2007 October; 97(10): 1746-1754.
- Heike A Bischoff Ferrari, Edward Giovannucci, Walter C Willett, Thomas Dietrich, Bess Dawson Hughes.Estimation of optimal serum concentrations of 25hydrox. Am J Clin Nutr July 2006 vol. 84 no. 1 1828.
- Leidig-Bruckner G, Roth HJ, Bruckner T, Lorenz A, Raue F, Frank-Raue K. Are commonly recommended dosages for vitamin D supplementation too low? Vitamin D status and effects of supplementation on serum 25-hydroxyvitamin D levels--an observational study during clinical practice conditions. Osteoporos Int. 2011 Jan;22(1):231-40. doi: 10.1007/s00198-010-1214-5.
- Amir E, Simmons CE, Freedman OC, Dranitsaris G, Cole DE, Vieth R, Ooi WS, Clemons M. A phase 2 trial exploring the effects of high-dose (10,000 IU/day) vitamin D(3) in breast cancer patients with bone metastases. Cancer. 2010 Jan 15;116(2):284-91. doi: 10.1002/cncr.24749.
- Vitamin D Council. For health professionals: Position statement on supplementation, blood levels and sun exposure. Vitamin D Council Fact Sheet.
- Kurt A. Kennel, MD, Matthew T. Drake, MD, PhD, and Daniel L. Hurley, MD. Vitamin D Deficiency in Adults: When to Test and How to Treat. Mayo Clin Proc. Aug 2010; 85(8): 752-758.
†Results may vary. Information and statements made are for education purposes and are not intended to replace the advice of your doctor. If you have a severe medical condition or health concern, see your physician.