Introduction and background

Roughly 1 in 5 Americans over the age of 40 have reported some alteration in their taste, according to the National Institutes of Health (NIH) [1]. The different kinds of taste alteration can be classified into complete and partial. Partial taste alteration is much more common than complete. The 2 types of partial taste alteration are dysgeusia and hypogeusia. Dysgeusia is a condition where a foul, metallic, or rancid taste occurs in the mouth [2], 3]. Around 1 in 20 Americans report dysgeusia, and most of these cases are reported by women (64 %) [2], 3]. Hypogeusia is a condition where people experience a reduced sense of taste. This condition is rare compared to dysgeusia. An extreme case of taste alteration is complete taste loss. This is also known as ageusia. Ageusia is the least common when compared to other taste conditions. About 1 or 2 in 1,000 people experience ageusia (0.001 %) [1], [3], [4], [5], [6].

The tongue plays an important role in picking up and transmitting taste sensations to the brain. It picks up 5 basic flavors, which are sweet, sour, salty, bitter, and savory, or “umami,” using receptors called taste buds to transmit these flavors to the brain. The brain then interprets and assigns flavors to these. There is a common myth that certain parts of the tongue pick up certain tastes more than others, but surprisingly, this is not true. All taste receptors across the tongue interpret all flavors. However, the sides and tip of our tongue are generally more sensitive to taste than the middle [7], 8].

Diagnoses with any form of taste loss are usually related to damage or impairment of nerves related to the pathway of taste from the tongue to the brain. The cranial nerves transmit signals from the tongue to the brain. They include the facial nerve, vagus nerve, and the glossopharyngeal nerve. The facial nerve is responsible for transmitting taste sensations from the anterior portion of the tongue, while the glossopharyngeal nerve transmits the sensation of taste from the posterior portion of the tongue. The vagus nerve is responsible for the taste sensations in the very back of the mouth, known as the epiglottis [7].

There may be many factors contributing to alterations in taste. Some of the most common factors are respiratory and ear infections, poor oral hygiene, dental problems, exposure to chemicals such as insecticides certain medications, and head injury [9]. One of the most common causes of taste problems is a loss of olfactory sensation. According to an article from the American Academy of Family Practice, 95 % of taste disorders are caused by an impairment of smell [3]. This is because the human body’s taste and smell are linked through chemosensation, the body system used to sense chemicals. When eating food, the molecules of food reach the back of the nose and interact with olfactory receptors (termed retro-nasal olfaction) [10]. This is why smell plays such a big part in taste. The remaining 5 % of taste issues are likely multifactorial in nature. One of the potential mechanisms underlying taste problems is biochemical or hematologic abnormalities, which is the focus of our research paper.

Biochemical markers are organic molecules like proteins, enzymes, electrolytes, lipids, micronutrients, inflammatory markers, or hormones found in blood, body fluids, or tissues that, when perturbed, can create an abnormality in biological processes. Hematological markers are measurements related to blood cells and their properties. Research on the relationship between biochemical or hematological markers, and loss of taste is limited. A study from 2021 described the relationship between patients diagnosed with COVID-19-related taste impairments and biochemical abnormalities. This study had patients rate their taste sensation on a visual analogue scale from 0 to 10, where a score of 0 indicated complete loss of taste (ageusia), while a score of 10 meant that there were no impairments to taste. Compared to patients who had normal taste, those with any degree of taste loss (VAS score<10) had a significantly lower neutrophil count and a higher lymphocyte count [11].

The relationship between biochemical markers and the taste loss is not fully understood. A handful of biochemical factors and their association with taste problems have been reported, but large scale epidemiologic studies supporting a cause-effect relationship are lacking. One vitamin that has shown a clear correlation with taste dysfunction is vitamin B12. The epithelial cells are responsible for being a protective cover for the body. A deficiency of vitamin B12 can cause a disruption in these cells, which in turn can lead to tongue pain, redness, and reduction in the number of papillae [12]. Some of the other biochemical taste markers that have been reported to contribute to taste loss include zinc and iron [13].

Examining the relationship between biochemical and hematological markers, and taste impairment can be immensely beneficial to the prevention and treatment of taste disorders. To address the gap in knowledge about how these markers may be associated with taste dysfunction, we conducted the current study, where we used a publicly available nationally representative database of participants who were asked a question about taste problems in the past year. We compared a large group of biochemical and hematological markers between those who did vs. those who did not experience taste problems in the past one year to identify potential associations. By exploring this area, our research could aid in the treatment and prevention of taste disorders.