Which of the following conditions can result in a painful red tongue in a diabetic?

A painful red tongue in a diabetic individual is often associated with uncontrolled blood sugar levels. Diabetes can lead to various oral complications, including alterations in the oral mucosa and increased susceptibility to infections. Poorly controlled blood sugar levels can cause a range of inflammatory conditions in the oral cavity, including glossitis, which manifests as a swollen, red, painful tongue.

Additionally, high blood glucose can disrupt normal blood flow and may lead to changes in the quality of saliva, putting individuals at risk for further complications such as fungal infections (e.g., candidiasis), which can also cause discomfort and redness of the tongue. Therefore, maintaining good glycemic control is crucial in preventing these oral manifestations and discomfort.

The other options, while they can affect overall health, do not directly correlate with the specific presentation of a painful red tongue in the context of diabetes. Vitamin D deficiency is more commonly linked to bone health and may affect general well-being rather than specifically leading to a red tongue. Thyroid dysfunction can influence metabolism and energy levels but is not a primary cause of tongue changes in diabetes. Infections, although they can contribute to oral issues, are often secondary to the underlying problem of uncontrolled blood sugar.