Why do patients with anorexia nervosa often experience bradycardia?

Cardiac complications are common in anorexia nervosa (AN), with sinus bradycardia occurring in up to 95% of patients1,2. The mechanism of bradycardia in AN has yet to be clearly elucidated.

The predominant hypothesis posits that bradycardia is due to an increased cardiac vagal tone3,4, with a direct relationship observed between vagal tone and percent weight loss4. Additionally, sympathetic response may be altered through down-regulation of cardiac beta-adrenoceptors5. The physiologic response of lowering the resting heart rate through an increase in parasympathetic activity and sympathetic down-regulation leads to energy conservation in the fasting state of AN.

Current guidelines recommend that patients with AN and “severe” sinus bradycardia—defined as heart rate <50 beats/min during the day or <45 beats/min at night—should be admitted to the hospital for cardiac monitoring and gradual weight gain6. Fortunately, bradycardia associated with AN is reversible with weight gain7,8.

 

References

  1. Portilla MG. Bradycardia: an important physical finding in anorexia nervosa. J Ark Med Soc 2011;107:206-208. https://www.ncbi.nlm.nih.gov/pubmed/21739848
  2. Katzman DK. Medical complications in adolescents with anorexia nervosa: a review of the literature. Int J Eat Dis 2005; 37:S52-S59. https://onlinelibrary.wiley.com/doi/full/10.1002/eat.20118
  3. Petretta M, et al. Heart rate variability as a measure of autonomic nervous system function in anorexia nervosa. Clin Card 1997; 20: 219-224. https://www.ncbi.nlm.nih.gov/pubmed/9068906
  4. Kollai M., et al. Cardiac vagal hyperactivity in adolescent anorexia nervosa. Eur Heart J 1994;15:1113-1118. https://www.ncbi.nlm.nih.gov/pubmed/7988604
  5. Kaye WH, et al. Isoproterenol infusion test in anorexia nervosa: Assessment of pre-and post-beta-noradrenergic receptor activity. Psychopharm Bull 1990.
  6. Golden NH, et al. Eating disorders in adolescents. J Adolesc Health 2003;33: 496-503. https://www.ncbi.nlm.nih.gov/pubmed/14642712
  7. Gottdiener JS, et al. Effects of self-induced starvation on cardiac size and function in anorexia nervosa. Circulation 1978;58: 425-433. https://www.ncbi.nlm.nih.gov/pubmed/679432
  8. Olivares JL, et al. Cardiac findings in adolescents with anorexia nervosa at diagnosis and after weight restoration. Eur J Pediatrics 2005;164:383-386. https://www.ncbi.nlm.nih.gov/pubmed/15909184

 

Contributed by Marissa K Shoji, Medical Student, Harvard Medical School

Why do patients with anorexia nervosa often experience bradycardia?

Why doesn’t excessive ingestion of carrots cause yellow discoloration of the sclera?

Great question! “Carotenoderma” refers to the yellow discoloration of the skin caused by increased serum carotenoids1.  Carotenoids are absorbed by passive diffusion from the gastrointestinal tract which are partially metabolized in the intestinal mucosa and liver to vitamin A, and then transported in the plasma into the intercellular lipids of stratum corneum of the skin which has a high affinity for carotene1,2.

The maximal accumulation of carotenoids occurs in areas with an abundance of sweat glands (eg, the palms, soles, nasolabial folds). In the absence of strateum corneum, the sclera is spared!

Of note, there are many causes of carotenoderma besides excessive ingestion of carrots.  Among foods, increased ingestion of tomatoes, tangerines, red palm oil, and squash may also be responsible1,2

Systemic diseases associated with increase in serum carotenoids (possibly related to decreased conversion to vitamin A, hyperlipidemia, or other factors) include hypothyroidism, diabetes mellitus, anorexia nervosa, nephrotic syndrome, and liver disease.

References 

  1. Horev L, Ramot Y, Klapholz L. Yellow feet in a patient with breast and thyroid carcinoma, due to oral intake of turmeric. Drug Saf-Case Rep 2015;2:4.https://link.springer.com/article/10.1007/s40800-015-0006-4
  2. Maharshak N, Shapiro J, Trau H. Carotenoderma-a review of the literature. Int J Dermatol 2003;42:178-181. http://onlinelibrary.wiley.com/doi/10.1046/j.1365-4362.2003.01657.x/epdf

 

Contributed by Clara Yang, Medical Student, Harvard Medical School

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Why doesn’t excessive ingestion of carrots cause yellow discoloration of the sclera?