Mgt 111 Vitamin D: How Much?

[michael edward badolato jr]

Caucasian skin may have evolved with the northern movement of humans over thousands of years. The light color - minimum melanin - allows picking up maximum UV rays for vitamin D synthesis - and storage life in tissue and plasma allows for 100 days of weaker winter sunshine which will not generate vitamin D. However, it seems that with a longer lifespan the lighter skin is often not durable enough to take sun exposure necessary to maintain optimal vitamin D  without skin damage or cancer. It may be possible to obtain vitamin D exclusively from the sun safely - but for many individuals and circumstances a supplement may be needed.

 

Generally supplements may not be a good idea because they present a concentration out of natural matrix that may interfere with metabolism of other nutrients - or present a toxic effect. Vitamin D  may be an exception because of the peculiar dilemma posed in obtaining the vitamin.

Much of the population has marginal vitamin D status - many falling below what is considered minimum optimal: a plasma 25OH-D level of 20 ng/ml or 50 nmol/L (1 ng/ml= 2.5 nmol/L). Minimum sun exposure has come to be defined as approx. 8ng/ml or 20 nmol/L. Low average in the population may be only about 18 ng/mL (45 nmol/L). Optimal may be between 60 and 75 nmol/L although some have proposed it should be 84 nmol/L.

At a starting point of 20 nmol/L - considered to be minimum sun exposure - a supplemental dose of 600 iu has a dose response curve of approx. 2.3 - raising plasma 25OH-D 2.3 nmol/L per 40 iu dose. 40 divided into 600 iu = 15 x 2.3 = 34 nmol/L plus the initial 20 equals 55nmol/L.

An additional 400 iu (total 1000) at the higher baseline of 55 nmol/L has a dose response curve of approx. 1.0 - 1 nmol/L per 40 iu dose so the additional 400 iu adds 10 nmol/L to bring plasma 25OH-D to 65 nmol/L. Another 400 iu (total 1400) at a slope of approx. .8 nmol/L per 40 iu brings 25OH-D to near 73 nmol/L.

 

With minimum sun exposure - a starting point of plasma 25OH-D at approx. 20 nmol/L, 1000 iu daily supplement vitamin D3 in liquid softgels may be appropriate.

With some sun exposure (low average) take less - such as approx 600 iu.

If lots of time in the sun - don't take supplemental vitamin D.

 

Plasma 25OH-D begins with a steep rise and levels off within 6 weeks of any maintained added dose level. For example, 25OH-D beginning at 20 nmol/L would level off at approx. 55nmol/L by 6 weeks in most people with the maintenance of a 600 iu daily dose.

At a baseline of 73 nmol/L and doses still higher than 1400 iu the dose response curve continues to fall off - eventually to only .6 nmol/L per 40 iu dose.

 

There is individual variability in plasma 25OH-D dose response, however it may not be good to adjust dose with intent to obtain a certain plasma 25OH-D level. It may be better to go on the optimal average for the group - thought to be appropriate and safe.

Cause of the individual variability is poorly understood. For example, those getting apparently similar ample amounts of sunshine have been found to have widely different plasma 25OH-D levels - with explanation for this broad and speculative (Binkley 2007). With vitamin D supplemental doses there seems little wastage - vitamin D finds its way in other metabolic forms and places than just as plasma 25OH-D.

 

The Food and Nutrition Board of the National Academy of Science (US RDA & DRI), recommended 200 iu vitamin D  per day in 1989 - increased the recommendation to 400 iu in 2006 - then to 600 iu in 2010 based on minimum sun exposure. Earlier recommendations not being correct - the 600 iu recommendation may be a little low. Some other recommendations may be somewhat incorrect also. Vitamin C is advised at 60-90 mg/day - 200 mg may be better. Potassium is at 4500 mg when 78 mg per 100 kcal (about 2400 on a 3000 or 3200mg on a 4000 kcal diet) may be all that is necessary. Sodium is at 1500 when 500-800 may be better.

 

The sun will not promote vitamin D synthesis 20 days annually for every 70 miles north of 40 degrees latitude at 5000 feet (ex. Denver) or 20 days for every 70 miles north of 35 degrees at sea level. Each 1000 feet of altitude = 70 miles = 1 degree of latitude. For example, 45 degrees north at 5000 feet and 40 degrees north at sea level (ex. Philadelphia) there are approx. 100 days each year with no vitamin D synthesis from the sun (approx. Nov 1 - Feb 10). However, the vitamin is stored in tissue - and plasma 25OH-D gradually decreases.

 

References 

Binkley et al. Low vitamin D status despite abundant sun exposure. J Clin Endocrin 92(6) 2130-35 2007

Bischoff-Ferrari H.A. et al. Higher 25-hydroxyvitamin D concentrations are associated with better lower extremity function in both active and inactive persons aged >60 years. Am J Cl Nutr 80:752-58 2004

Bischoff-Ferrari H.A. et al. Positive association between 25 hydroxyvitamin D levels and bone mineral density: a population based study of younger and older adults. Am J Med 116: 634-39 2004

Bischoff-Ferrari H.A. et al. Fall prevention with supplemental and active forms of Vitamin D: a meta analysis of randomized controlled trials. BMJ 2009 Oct 1; 339:b3692doi:10.1136/bmj.b3692

Cashman K.D. et al. Low vitamin D status adversely affects bone parameters in adolescents. Am J Cl Nutr 87:1039-44 2008

Cashman K.D. et al. Estimation of the dietary requirement for vitamin D in healthy adolescent white girls. Am J Cl Nutr 88: 1535-42 2008.

Cashman K.D. et al. Estimation of the dietary requirement for vitamin D in free living adults >64 y of age. Am J Cl Nutr 89: 1366-74 2009

Dietary Supplement Fact Sheet: http://ods.od.nih.gov/factsheets/vitaminD

Harris S.S. and Dawson Hughes B. Plasma vitamin D and 25OHD responses of young and old men to supplementation with vitamin D3. J Am Coll Nutr 21(4): 357-62 2002

Institute of Medicine, Food and Nutrition Board, Dietary Reference Intakes for Calcium and Vitamin D, Washington D.C., National Academy Press, 2010

Lehtonen-Veromaa M.et al. Vitamin D and attainment of peak bone mass among peripubertal Finnish girls: a 3 year prospective study. Am J Cl Nutr 76: 1446-53 2002

Liu E. et al. Predicted 25-hydroxyvitamin D score and modest type 2 diabetes in the Framingham Offspring Study. Am J CL Nutr 91: 1627-33 2010

Patel R. et al. The effect of season and vitamin D supplementation on bone mineral density in healthy women: a double crossover study. Osteoporosis Int 12(4): 319-25 2001

Pfiefer M. et al. Effect of a short term vitamin D and calcium supplementation on body sway and secondary hyperthyroidism in elderly women. J Bone Mineral Reserve 15(6): 1113-18 2000

Tuohimaa P. et al. Both high and low levels of blood vitamin D are associated with a higher prostate cancer risk: a longitudinal nested case-control study in the nordic countries. Int J Cancer 108: 104-08 2004

Tylavsky F.A. et al. Preliminary findings; 25OHD levels and PTH are indicators of rapid bone accrual in pubertal children. J Am Coll Nutr 25;:5 429-35 2006

Urashima M. et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in school children. Am J Cl Nutr 91: 1255-60 2010

Viljakainen H.T. et al. How much vitamin D3 do the elderly need. J Am Coll Nutr 25;5: 429-35 2006

Viljakainen H.T. et al. A positive dose response effect of Vitamin D supplementation on site specific bone mineral augmentation in adolescent girls; a double blind randomized placebo-controlled 1 year intervention. J Bone Miner Res 21; 836-44 2006

Wicherts I.S. et al. Vitamin D status predicts physical performance and its decline in older persons. J Clin Endocrin 92(6) 2058-65 2007