About 25-50% of Americans are deficient in vitamin D mostly because they spend little or no time in the sun. The sun's UV rays allow the skin to synthesize vitamin D so sunscreens and clothing that block the UV rays also block vitamin D synthesis. For many years it has been known that too little vitamin D leads to weak bones. Vitamin D is also needed for proper immune function and cell differentiation and a deficiency increases the risk of several types of cancer and some autoimmune diseases like type 1diabetes and multiple sclerosis.
More recently, data is mounting that a lack of vitamin D may contribute to cardiovascular disease (CVD). Too little vitamin D has been associated with the calcification of arteries, the proliferation of vascular smooth muscle cells, increased blood pressure and heart failure. This is consistent with other data showing higher rates of hypertension and cardiovascular disease (CVD) in people who live farther away from the equator.1
A new study looked at vitamin D status and then followed more than 1,700 people in the Framingham Health Study for an average of 5.4 years to determine if there was a relationship between low 25-hydroxy vitamin D (25-OH D) status and CVD events. The 28% of subjects with a 25-OH D level below 15ng/ml were 62% more likely to have a heart attack, stroke, or other CVD event during the follow-up period after correcting for other CVD risk factors. Nearly all of this increased risk of CVD events was concentrated in the 40% of subjects who had hypertension. In those with hypertension and low levels of 25-OH D in the blood their risk of suffering a CVD event was more than doubled.
Bottom Line: There is already plenty of evidence linking low levels of sun exposure and an inadequate intake of vitamin D from foods and supplements with numerous adverse effects on health. In older people the only vitamin supplement shown to increase life expectancy was vitamin D. For those who live in the northern US and those who get little sunshine a dietary supplement of at least 1000 to 2000 IU per day makes sense. It is likely Americans could cut their risk of CVD with a little sunshine and/or vitamin D supplements.
By James J. Kenney, PhD, RD, FACN
1. Lancet 1989;1:613
Stephanie Ronco has been editing in a professional capacity for the past 10 years. In addition to her work as an editor, Ronco has also served as a ghostwriter and writing tutor. A voracious reader, Ronco loves watching language evolve and change. When she’s not delving into her latest project, Ronco can be found teaching acting classes, performing in community theater, or sailing with her husband.