Starfruit and Fluoride: What do they have in common?
I want to preface this post with the fact that this likely has only a smidge of dentistry unless you consider that my first experience with starfruit was in a dental office. Almost all areas of science have a place in dentistry if you ask me, so todays post is more about Toxicology and less about dentistry. I feel understanding Toxicology is very important, especially for dental hygienists as I have been confronted with multiple claims regarding substances, we use in dentistry being “toxic.” So, this post is an effort to highlight how interesting toxicology can be, its relevance to dentistry, as well as to highlight the fact that “natural” isn’t always safer or better. This is a story about starfruit and my subsequent understanding of the toxic effects of this delicious fruit and what it has in common with fluoride.
My co-worker and friend, we will call her Amy because that is in fact her name, was eating starfruit at the office one day. I had never eaten starfruit, I’m not sure why, it is just generally not on my grocery list. So, I tell my co-worker/friend that I’ve never tasted starfruit. Being the kind and generous person that she is, she offered me a piece or two to try. It indeed was quite tasty, and I was a little disappointed I hadn’t tried it before now. At the time I was taking a toxicology course, and though this toxicology course did not go deep into specific substances, it was enough to get me really interested in the subject. With that burning desire to learn more, I started listening to every toxicology podcast I could find as well as reading blogs by toxicologists. I had a deep desire to understand this subject well enough to be able to share the knowledge I was gaining. One of my favorite blogs I found is Nature’s Poison, the author is a toxicologist, and he focuses on poisons that are found in nature. It is truly fascinating.
Back to starfruit, the author Dr. Justin Bower, a Forensic Toxicologist, wrote a bit about starfruit. Here is what I learned from his post.
1. Long-term hiccups (lasting more than 48 hours) could be associated with irritation of the vagus nerve. Additionally, long-term hiccups may be a sign of a more serious underlying condition such as MS, encephalitis, stroke and kidney failure. Oh, and starfruit could be the culprit as well.
2. Starfruit can be neurotoxic, nephrotoxic, and in some cases, fatal 
Wait a second, what?!? Neurotoxic, nephrotoxic and fatal, and they sell it all willy nilly in the grocery store? The neurotoxin found in starfruit is caramboxin, it is metabolized in the kidneys. For people that are in kidney failure or are on dialysis this neurotoxin can build up and cause signs of neurotoxicity, one such symptom is the hiccups. However, don’t get all high and mighty if you have proper kidney function because there have been studies that show people with normal renal function can be affected by starfruit consumption. In one such case study 5 patients with previously normal renal function were diagnosed with acute renal failure after consuming large amounts of starfruit.
This all sounds somewhat scary, doesn’t it? Much like the claims made about fluoride and other substances used in dentistry. Does all this mean we should never eat starfruit? Of course not, this goes back to the central tenant of toxicology; dose makes the poison. Just as proper doses of fluoride are completely safe, reasonable doses of starfruit are safe as well. Both are considered neurotoxins, but that doesn’t mean that neurotoxicity will occur from reasonable exposures. Our bodies are well equipped to manage a certain level of toxic substances. If you have a functioning kidney, starfruit is likely to be a treat that you can enjoy.
I know helping patients understand this concept may be difficult, but a start would be in helping dental professionals understand this concept. Too often I see dental professionals making bold claims about substances being toxic with no mention of dose, time or bioavailability all very relevant in determining if a substance poses a risk to one’s health. Not all things that are considered “toxic” are inherently dangerous, and not all things that are considered “natural” are inherently safe. If you are interested in learning more about Toxicology and nature, I highly recommend reading Dr. Justin Bowers blog, Nature’s Poison, he is a great writer, and the content is very valuable. If you are a dental professional that hasn’t taken Toxicology, but is interested in learning more about its relevance in dentistry….stay tuned, I’m diligently working on a continuing education course just for you!
1. Nature’s Poison, Starfruit: Which Came First, the Hiccups or Kidney Failure. Retrieved from https://naturespoisons.com/2015/10/01/starfruit-which-came-first-the-hiccups-or-the-kidney-failure-caramboxin/
2. Neto MM, da Costa JA, Garcia-Cairasco N, Netto JC, Nakagawa B, Dantas M. Intoxication by star fruit (Averrhoa carambola) in 32 uraemic patients: treatment and outcome. Nephrol Dial Transplant. 2003;18(1):120-125. doi:10.1093/ndt/18.1.120. Retrieved from https://pubmed.ncbi.nlm.nih.gov/12480969/
3. Neto MM, Silva GE, Costa RS, et al. Star fruit: simultaneous neurotoxic and nephrotoxic effects in people with previously normal renal function. NDT Plus. 2009;2(6):485-488. doi:10.1093/ndtplus/sfp108. Retrieved from https://pubmed.ncbi.nlm.nih.gov/25949386/