Here in the UK, until very recently, we’ve had something of a heat-wave. The sun has been shining brightly on most days and this is good news for me, as I’ve been able to take advantage of the opportunity to boost my vitamin D levels. Why is this important? Because higher vitamin D levels are associated with protection from a range of conditions including several forms of cancer, cardiovascular disease, multiple sclerosis, and bone disease, and also appears to have positive influence on factors such as muscle health and physical fitness.
The importance of maintaining optimal vitamin D levels was brought home to me again on the publication recently of a study of more than 3400 individuals aged 65 and over [1]. These individuals were monitored for more than 7 years, during which death from cardiovascular disease (e.g. heart attacks and stroke) and overall risk of death were recorded. Study participants their vitamin D levels measured at the beginning of the trial too. This allowed the researchers to assess the relationship between vitamin D levels and overall risk of death in the time period the study ran for.
What they discovered is that lower levels of vitamin D were associated with an increased risk of death, especially from cardiovascular disease.
Compared to individuals with a vitamin D level of 40 ng/ml (100 mmol/l) or more:
Individuals with vitamin D levels 10.0 ” 19.9 ng/ml were at a 47 per cent increased risk of death overall
Individuals with vitamin D levels less than 10.0 ng/ml were at a 83 per cent increased risk of death overall
Individuals with vitamin D levels less than 10.0 ng/ml were at a 236 per cent increased risk of death from cardiovascular disease
Studies of this nature (so-called epidemiological) studies are good for identifying associations (e.g. vitamin D levels and risk of death) but cannot be used to conclude that one factor is causing the other (i.e. low vitamin D levels cause death). However, what is clear is that there is a very consistent body of evidence now linking higher vitamin D levels and reduced risk of disease and death.
A year ago, I blogged about a study which, again, found lower vitamin D levels to be associated with a significantly increased risk of death. You can read about that study here.
The authors of the more recent study that is the focus of this blog call for randomized controlled trials of vitamin D supplementation ‘to determine whether this association is causal and reversible’. In other words, if giving individuals vitamin D, compared to placebo, reduced risk of death, then we know that low levels of vitamin D can cause death, and that this can be remedied.
I fully support the idea of such trials. However, chronic conditions such as heart disease tend to have long ‘latency’, which means the processes that cause these conditions tend to go on for a long time before the condition manifests. For this reason, the trials are generally going to need to be long for any real benefits to be detected. In the meantime, we do have at least some evidence that suggests there is merit in maintaining optimal vitamin levels. In 2007 the Archives of Internal Medicine published last year a ‘meta-analysis’ which grouped together several studies where death rate in those supplemented with vitamin D (dosages ranged from 300 ” 2000 IU per day) was compared to the death rate in individuals taking placebo [3]. The vitamin D supplemented individuals overall were found to enjoy a small (7 per cent) but statistically significant reduction in risk of death.
Regular readers of this blog may know that I recently had my vitamin D levels checked. They came in at a thoroughly deficient 15 ng/ml. This, despite the fact that I make a point of spending as much time in the sun as possible, and have not worn used sunscreen for about 20 years. As a result, I have taken to supplementing with vitamin D (3000 IU per day) and have just sent off a sample to have my levels re-checked. I await the results with bated breath.
References:
1. Ginde AA, et al. Prospective Study of Serum 25-Hydroxyvitamin D Level, Cardiovascular Disease Mortality, and All-Cause Mortality in Older U.S. Adults. Am Geriatr Soc, 2009 June 22 [Epub ahead of print]
2. Dobnig H, et al. Independent Association of Low Serum 25-Hydroxyvitamin D and 1,25-Dihydroxyvitamin D Levels With All-Cause and Cardiovascular Mortality. Arch Intern Med. 2008;168(12):1340-1349
3. Autier P, et al. Vitamin D supplementation and total mortality. Arch Int Med 2007;167:1730-1737
