Vitamin D recommendations have been raised, but not enough

SupplementsA few weeks ago, the Institute of Medicine (IOM) surprised many of us when it announced its new dietary reference intake (DRI) for vitamin D. The consensus of the scientific community was that the previous DRI of 400 IU was insufficient, and that supplementation with at least 1000 IU would be necessary for most people to achieve vitamin D sufficiency. The IOM disagreed.

The IOM’s new recommendations:

- Recommended intake: 600 IU per day (for children and adults under age 70)

- Tolerable upper limit (amount not to be exceeded in one day): 4000 IU (raised from 2000 IU)

- Sufficient blood 25(OH)D level: 20 ng/ml

There has been a great deal of research in recent years on vitamin D’s role in a variety of human diseases. Low vitamin D status has been associated with cardiovascular disease, certain cancers, cognitive decline, depression, diabetes, pregnancy complications, autoimmune diseases, and even a 78% increase in all-cause mortality risk (<17.8 ng/ml 25(OH)D compared to >32.1 ng/ml). [1] However, because there are not yet enough randomized controlled trials to clearly and conclusively confirm the benefits of vitamin D supplementation for conditions unrelated to bone health [2], the IOM did not find the existing evidence for non-skeletal conditions sufficient enough to raise the daily recommendations any higher than 600 IU. The 600 IU figure is based solely on bone health - they did not take into account whether a greater quantity of vitamin D might be necessary to prevent non-skeletal diseases, even though there are vitamin D receptors in almost every cell of the human body.

Many experts are weighing in on – and disagreeing with – the IOM’s report, and there is general agreement among the experts on these points:

  • The increase of the tolerable upper limit to 4000 IU is a positive change.
  • The IOM’s definition of 20 ng/ml as a sufficient 25(OH)D is potentially low, and this could be dangerous for some people
  • The lack of randomized controlled trials does not mean that we should ignore the epidemiological evidence showing vitamin D’s importance for preventing non-skeletal diseases.

Compare my recommendations to those of the IOM:

Recommendations: 25(OH)D Vitamin D supplementation (adults)
Institute of Medicine >20 ng/ml 600 IU
Dr. Fuhrman 35-55 ng/ml 2000 IU*

*adjust supplementation according to 25(OH)D level

I agree that the IOM’s recommendations are inadequate. My recommendation is a safe, conservative amount of vitamin D which is supported by the literature. To learn more about why following the IOM’s guidelines may be risky, read my full commentary.

 

References:

1. Melamed, M.L., et al., 25-Hydroxyvitamin D Levels and the Risk of Mortality in the General Population. Archives of Internal Medicine, 2008. 168(15): p. 1629-1637.
2. Zhang, R. and D.P. Naughton, Vitamin D in health and disease: Current perspectives. Nutr J, 2010. 9(65).

 

Diet soda depletes the body's calcium stores

Soda drinking has previously been associated with lower bone mineral density in women and children1,2, and a new study focuses specifically on the effects of diet soda on bone health. The authors commented that this research was sparked by the observation that diet soda drinking behaviors are often different than regular soda drinking behaviors – women often use diet sodas in an effort to avoid weight gain – either to stave off hunger between meals or as a replacement for calorie-containing beverages. Many women drink over 20 diet sodas per week.3

The average American drinks 216 liters of soda each year.4

Pouring soda

These researchers discovered that parathyroid hormone (PTH) concentrations rise strongly following diet soda consumption. PTH functions to increase blood calcium concentrations by stimulating bone breakdown, and as a result release  calcium from bone.

In the study, women aged 18-40 were given 24 ounces of either diet cola or water on two consecutive days, and urinary calcium content was measured for three hours. Women who drank diet cola did indeed excrete more calcium in their urine  compared to  women who drank water. The authors concluded that this calcium loss may underlie the observed connection between soda drinking and low bone mineral density.5

Although caffeine is known to increase calcium excretion and promote bone loss6, caffeine is likely not the only bone-harming ingredient in sodas. A 2006 study in the American Journal of Clinical Nutrition found consistent associations between low bone mineral density and caffeinated and non-caffeinated cola (both regular and diet), but not other carbonated beverages.7 One major difference between the two is the  phosphoric acid in  colas, absent from most other carbonated beverages. 

In the Western diet, phosphorus is commonly consumed in excess – at about 3 times the recommended levels, whereas dietary calcium often low.  Although phosphorus is an important component of bone mineral, a high dietary ratio of phosphorus to calcium can increase parathyroid hormone secretion, which is known to increase bone breakdown.   Studies in which women were given increasing quantities of dietary phosphorus found increases in markers of bone breakdown and decreases in markers of bone formation.8,9 Therefore it is likely that the phosphorus content of colas,  triggers calcium loss.

There is nothing healthy about diet soda. It is simply water with artificial sweeteners and other chemical additives, such as phosphoric acid. The safety of artificial sweeteners is questionable, and their intense sweetness disrupts the body’s natural connection between taste and nourishment,  promoting weight gain.10 Diet sodas don’t just weaken our bones, they are linked to kidney dysfunction and promote obesity and other common medical problems.

 

References:

1. McGartland C, Robson PJ, Murray L, et al. Carbonated soft drink consumption and bone mineral density in adolescence: the Northern Ireland Young Hearts project. J Bone Miner Res. 2003 Sep;18(9):1563-9.

Mahmood M, Saleh A, Al-Alawi F, Ahmed F. Health effects of soda drinking in adolescent girls in the United Arab Emirates. J Crit Care. 2008 Sep;23(3):434-40.

2. Tucker KL, Morita K, Qiao N, Hannan MT, Cupples LA, Kiel DP. Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Study. Am J Clin Nutr. 2006 Oct;84(4):936-42

3. Frieden J. ENDO: Diet Soft Drinks Deplete Urinary Calcium. Medpage Today. http://www.medpagetoday.com/MeetingCoverage/ENDO/20831

5. NS Larson, et al "Effect of Diet Cola on urine calcium excretion" ENDO 2010; Abstract P2-198. http://www.endojournals.org/abstracts/P2-1_to_P2-500.pdf

6. Vondracek SF, Hansen LB, McDermott MT. Osteoporosis risk in premenopausal women. Pharmacotherapy. 2009 Mar;29(3):305-17.

Massey LK, Whiting SJ. Caffeine, urinary calcium, calcium metabolism and bone. J. Nutr. 19923 Sep;123 (9): 1611-14

7. Tucker KL, Morita K, Qiao N, et al. Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Study. Am J Clin Nutr. 2006 Oct;84(4):936-42.

8. Kemi VE, Kärkkäinen MU, Karp HJ, et al. Increased calcium intake does not completely counteract the effects of increased phosphorus intake on bone: an acute dose-response study in healthy females. Br J Nutr. 2008 Apr;99(4):832-9.

9. Kemi VE, Kärkkäinen MU, Lamberg-Allardt CJ. High phosphorus intakes acutely and negatively affect Ca and bone metabolism in a dose-dependent manner in healthy young females. Br J Nutr. 2006 Sep;96(3):545-52.

10. Swithers SE, Martin AA, Davidson TL. High-intensity sweeteners and energy balance. Physiol Behav. 2010 Apr 26;100(1):55-62. 

Sodium, acid-base balance, and bone health

 

We’ve known for years that excessive sodium intake contributes to hypertension, and a new meta-analysis of 13 studies has confirmed that high sodium intake is associated with increased risk of stroke and overall cardiovascular disease.1 Salt consumption is also associated with kidney disease, and a new study suggests that reduced sodium intake could benefit bone health.

Women 45-75 years old with prehyptertension or stage 1 hypertension were assigned to one of two diets.  Both diets supplied the same amount (800 mg) of calcium.  One diet was a high-carbohydrate, low-fat diet.  The other diet was a low-sodium diet (1500 mg), which included red meat but was designed to have a low acid load.2 

Western diets, generally high in animal protein, produce acid in the body, forcing the body to buffer this acid in part by the release of alkalizing salts from bone (e.g. calcium citrate and calcium carbonate) – this is associated with urinary calcium loss and is thought to contribute to osteoporosis. Fruits, vegetables, and legumes have favorable effects on acid-base balance, since the acid-forming effect of their protein content, which is lower than that of animal products anyway, are balanced by their mineral content.3-4

After 14 weeks, the women on both diets increased markers of bone formation and reduced their calcium excretion – those on the low sodium diet had a greater reduction in calcium loss. The authors concluded that this diet was protecting the mineral reserves in bone, and that this could have long-term implications for bone health. Future studies will likely measure bone mineral density and fracture incidence in response to these diets.2

The average daily consumption of sodium for Americans is around 4000mg, almost double the U.S. recommended maximum of 2300mg. The low sodium diet in this study provided a maximum of 1500mg of sodium per day, but included up to six servings of red meat per week, limited the consumption of nutrient-rich legumes to 4-5 per week, and was based on high-calorie, nutrient-poor grain products - 7-8 servings per day.5 The high-carbohydrate low-fat diet was likely based on grain products as well.

Although both of these diets had favorable effects when implemented in place of a standard western diet, they both have room for improvement. By minimizing the high-protein, high-saturated fat animal products, and replacing grain products with mineral- and phytochemical-rich vegetables, fruits, and legumes as the base of the diet, both acid load and sodium would be further reduced, presumably leading to further benefits on bone health.

 

References:

1. Strazzullo P et al. Salt intake, stroke, and cardiovascular disease: meta-analysis of prospective studies. BMJ 2009;339:b4567

2. Nowson CA et al. The effects of a low-sodium base-producing diet including red meat compared with a high-carbohydrate, low-fat diet on bone turnover markers in women aged 45-75 years. Br J Nutr. 2009 Oct;102(8):1161-70. Epub 2009 May 18.

3. Welch AA et al. Urine pH is an indicator of dietary acid-base load, fruit and vegetables and meat intakes: results from the European Prospective Investigation into Cancer and

Nutrition (EPIC)-Norfolk population study. Br J Nutr. 2008 Jun;99(6):1335-43. Epub 2007 Nov 28.

4. Massey LK. J Nutr. Dietary animal and plant protein and human bone health: a whole foods approach. 2003 Mar;133(3):862S-865S.

5. http://dashdiet.org/