Deficiency of fluoride leads to which one of the following health problems?

Fluoride is a naturally occurring mineral essential for dental health. Its primary benefit lies in strengthening tooth enamel, making it more resistant to acid attacks from bacteria and sugar [2]. Scientific evidence demonstrates that low concentrations of fluoride in drinking water (0-0.5 mg/L) are directly associated with increased rates of dental caries, also known as tooth decay [3]. Conversely, optimal fluoride levels (0.5-1.5 mg/L) are protective against this disease [1]. While deficiency leads to caries, excessive fluoride intake causes adverse health problems. High concentrations (>1.5 mg/L) lead to dental fluorosis, characterized by the mottling, staining, and pitting of teeth [1]. Chronic overexposure can also result in skeletal fluorosis, which manifests as the hardening of bones, bending of legs (Knock-Knee syndrome), and stiffening of joints [2]. Therefore, while options 2, 3, and 4 are results of fluoride toxicity, tooth caries is the specific result of its deficiency.

Sources

1. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > 3. Hazards of ground water pollution: > p. 76
2. [1] https://nora.nerc.ac.uk/13816/1/Fluor_FMF_NORA.pdf
3. [3] https://pmc.ncbi.nlm.nih.gov/articles/PMC6195894/