This month a group of Indian researchers reported their findings that supplementation of Vitamin C in guinea pigs exposed to cigarette smoke developed significantly less atherosclerosis (sometimes referred to as hardening of the arteries) than guinea pigs exposed to smoke without Vitamin C. (Ray T, et al. Vitamin C Prevents Cigarette Smoke Induced Atherosclerosis in Guinea Pig Model. J Atheroscler Thromb. 2010 May 13. [Epub ahead of print])
Prolonged exposure to cigarette smoke has previously been shown to be a significant risk factor in the development of atherosclerosis in humans. Atherosclerosis is characterized by thickening of artery walls and build-up of cholesterol plaques in the arteries which over time can block blood flow and cause cardiac events.
You might ask – what does a Vitamin C study about cigarette smoking guinea pigs have to do with humans who smoke? A good question. According to the study authors, guinea pigs are a good proxy for humans when it comes to atherosclerosis due to the fact that cholesterol is distributed in the arteries in very similar ways in both species. Further, similar inflammatory responses to cigarette smoke in humans and guinea pigs has been previously studied and documented. Finally, guinea pigs apparently cannot synthesize Vitamin C from their diet and so nutritional supplementation is the only source of Vitamin C a guinea pig can absorb which makes it easier to isolate its effects.
Cigarette smoke contains massive numbers of free radicals which are considered pro-oxidants (chemicals which damage human tissue unless counteracted by antioxidants such as Vitamin C). Over time, if a person does not have adequate antioxidant levels in their body to overcome the presence of free radicals, diseases such as atherosclerosis can develop. It is clear from past research studies that smokers have depressed antioxidant levels due to the pro-oxidants inhaled in smoke and it is equally clear that atherosclerosis is common among smokers.
So with that in mind, the researchers discovered that cigarette smoke increased the thickness of the guinea pig aortas and increased a body mechanism known as apoptosis (in simple terms, programmed cell death) in the epithelium (lining of the arteries). This, according to the researchers, led to a notable build-up of cholesterol deposits in the guinea pig arteries and proved a clear diagnosis of atherosclerosis after 21 days of cigarette smoke exposure.
By contrast, guinea pigs that were exposed to cigarette smoke for 21 days and provided a Vitamin C supplement each day had significantly less aortic wall thickening, significantly less shedding of epithelial cells, and significantly less cholesterol plaque build-up in the arteries. Indeed, the researchers concluded that those guinea pigs who consumed Vitamin C each day had not developed atherosclerosis.
The study authors conclude, “Therefore, our findings provide insight into some critical atherogenic events triggered by cigarette smoke in the guinea pig model, which is one of the first of its kind and also establishes the preventative role of Vitamin C in the development of the disease.”
The guinea pigs in the study were provided either 1mg or 5 mg of Vitamin C each day. That obviously is inadequate for humans. The National Academy of Sciences (NAS) recommended Vitamin C daily intake (now referred to as Dietary Reference Intake) for average adults is 90mg but given the huge amount of pro-oxidant chemicals inhaled in cigarette smoke, this level is not protective for smokers. We are unaware of any specific dosage recommended for smokers but the tolerable upper level limit recommended by the NAS is 2,000 mg each day. A number of studies on Vitamin C for its antioxidant protection have been done on dosages between 500mg and 1,000mg per day. Supplemental Vitamin C, in the form of ascorbic acid, is widely available online and in retail stores for $3-$10 per 30 day supply depending on the dosage level chosen.
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