Dr. Eric Berg (on YouTube) has a video about how different deficiencies affect hair and nails. He mentions that horizontal ridges across the nails are linked to Vitamin B1 (Thiamin) deficiency, and that can be linked to the consumption of highly processed grain and flour products that are not only lacking many nutrients, but that also force the body to have to utilise a great amount in order to be processed through the digestive system. Beri-beri was first discovered in groups that ate mainly white polished rice that was also missing the germ - the most nutritious part. These are foods that rob far more out of the body than they give.
I can testify to that as the very deep horizontal furrows in my thumb nails went away after I dumped gluten grains and most carbs and added in some decent supplements including B complex and extra Thiamin.
I am still trying to rectify the vertical ridges. They can apparently be linked to thyroid issues, but I suspect they are more likely to be linked to the deficiencies that trigger thyroid issues. Not caused by the Thyroid issues but a part of the same issue. Some have mentioned that taking Synthroid etc. has not stopped the ridges, but that may be because the Synthroid addresses the Thyroid symptoms but not necessarily the cause.
I can testify to that as the very deep horizontal furrows in my thumb nails went away after I dumped gluten grains and most carbs and added in some decent supplements including B complex and extra Thiamin.
I am still trying to rectify the vertical ridges. They can apparently be linked to thyroid issues, but I suspect they are more likely to be linked to the deficiencies that trigger thyroid issues. Not caused by the Thyroid issues but a part of the same issue. Some have mentioned that taking Synthroid etc. has not stopped the ridges, but that may be because the Synthroid addresses the Thyroid symptoms but not necessarily the cause.