Epidemiologic studies have shown an inverse relationship between presence of various cancers and dietary carotenoids or blood carotenoid levels. However, several trials using в-carotene supplements did not show protective effects against cancer or cardiovascular diseases. On the contrary, the high risk population (smokers and asbestos workers) in these trials showed an increase in cancer and angina. It appears that carotenoid can promote health when taken at dietary levels, but may have adverse effects when taken in high dose by subjects who smoke or who have been exposed to asbestos. In nonmelanoma skin cancers primarily consisting of basal cell and squamous cell carcinomas, the effect of в -carotene on cancer prevention is inconsistent. The beneficial effect of carotene-rich food in nail abnormalities, as seen in our patients, may be due to a combination of different carote- noids. It may be the task of ongoing and future studies to define the populations that can benefit from carotenoids and to define the proper dose and length of treatment.
Biologic mechanisms of such protection are currently unclear but several possibilities exist: certain carotenoids 1) can convert to retinoids, 2) can modulate the enzymatic activities of lipooxy- genases (proinflammatory and immunomodulatory molecules), 3) can have antioxidant properties which are well above those seen with vitamin A, 4) can activate the expression of genes which encode the message for production of connexin 43, which is an integral component of the gap junctions required for cell to cell adhesion. viagra 50 mg
Regarding the effect on skin diseases, в-carotene has been successfully used to treat photosensitivity in patients with erythropoietic protoporphyria but it only slightly increases the sunburn threshold in normal humans. Benefits are not seen typically until a few months after therapy is initiated and dosages of up to 180 mg/day is recommended. It is therefore possible that photoprotection is mediated through an alternative mechanism other than a direct sunscreen effect.
The reported side effects after ingestion of carotene rich food are visible yellowing of the skin, diarrhea and orange or rusty discoloration of the stool. The side effects are tolerable and are not indications for discontinuing treatment.
Hsu and Huang previously reported that intake of carotene rich-food in two patients with prolonged histories of chronic idiopathic onycholysis showed dramatic improvement of onycholysis in 3 months. As far as we know, there have been no studies regarding the effect of carotene on nail disorders. However, from the results of Hsu and Huang and the improvements seen in our patients, we propose that carotene may have a role in normal epithelial differentiation and keratinization of the nail plate or photoprotection of the nail bed. Since there are no reliable treatment methods, we suggest a simple and compliant method consisting of taking carotene-rich food in patients with chronic idiopathic onychody- strophy. A further study with carotene-rich food supplements or quantitative intake of specific carotenes to verify their effect on nail formation is needed.