The Indispensable Vitamin From the SUN
by Jolie Martin Root, L.N.C.

As critical as calcium?
Low levels of vitamin D are linked to both muscle weakness, risk of falls, and bone fractures. A brand new study in May of 2012 found that lower vitamin D levels were associated with worse coordination and weaker strength in older women, slower walking time, and a reduced upper limb strength in older men, and a weaker aerobic capacity in both genders. The researchers found that for optimal physical strength, 25 OH D concentrations should be at least 40 ng/ml in elderly men and women, and vitamin D supplementation should be encouraged to maintain this 25 OH D level.

Bone health is dependent on a dynamic process of remodeling which requires adequate vitamin D. Most people think of calcium when they think of strong bones, but vitamin D is equally as crucial. When vitamin D levels are deficient, the result is rickets in children and osteomalacia or osteoporosis, meaning soft or porous bones, in adults.

The rest of the vitamin D story
Bone health is only a fraction of the vitamin D story, as demonstrated by a steady stream of published research. Low levels have been linked to higher risk of autoimmune disease, infectious disease, chronic inflammation, and cardiovascular disease.

Increasing evidence suggests that vitamin D benefits both innate and adaptive immunity, thereby eliciting an anti-inflammatory effect and reducing the risk of infectious disease. A recent study found that having vitamin D levels greater than 30ng/ml cut the risk of chronic bronchitis in half compared to having a deficiency. Respiratory infection rates in children also point to the immune benefit of having adequate vitamin D levels. Children who are at the deficiency level of <10 ng/ ml have 11 times more respiratory infections than children who have levels of 30ng/ml or higher.

A Harvard School of Public Health study found an association between vitamin D levels and the risk of heart attacks. The study published in the Archives of Internal Medicine showed that a person who had a 30ng/ml blood level of vitamin D had half the risk of a heart attack compared to a person whose level was 15 ng/ml. The vitamin has been linked to a broad range of cardiovascular benefits including a reduced risk of peripheral arterial disease (PAD), a reduced risk of hypertension, and a reduced risk of stroke.

Determining optimal D levels
Vitamin D levels that are low have even been linked to increased risk of death, no matter what the cause. A 2012 meta-analysis examined vitamin D status and all-cause mortality and found that an 8 ng/ml increase in vitamin D was associated with 8% lower mortality risk in the general elderly population.

Although a consensus regarding the optimal level of serum 25(OH)D is still in debate, most experts define vitamin D deficiency as a 25(OH)D level of < 20 ng/ ml and vitamin D insufficiency as < 30ng/ml. Some experts believe that 50 ng/ml should be the target level. Vitamin D testing is becoming routine by most physicians, but in case testing isn't convenient, maintaining adequate levels typically requires an intake, in adults, of at least 4000 IUs of cholecalciferol or vitamin D3 daily.

References:
Edward Giovannucci, MD, ScD, et al. Arch Intern Med. 2008; 168(11):1174-1180.
Zhao G, et al. Br J Nutr. 2012; 107:1386-92.
Wayse V, et al. European Journal of Clinical Nutrition 2004; 58: 563–567.
Michal L. Melamed, et al. Arteriosclerosis, Thrombosis, and Vascular Biology. 2008; 28:1179
Schöttker B, et al. Ageing Res Rev. 2012 Feb 17