Did you know that Vitamin D is one of the only vits that acts like a hormone in your body and helps regulate your endocrine system? Think of it as helping to oil the engine that is your immune system.
Many coeliacs are deficient in Vitamin D upon diagnosis but not all are followed up correctly nor have their levels monitored. Here's some stats from the HU forum here to give you a snapshot of the symptoms low vitamin D can cause (see pic). For example, it has been linked to weight gain, cramps, aches, stiffness, osteomalacia and hormonal imbalances. Anyone with Endometriosis & Coeliac should double check their levels with their GP. It's a crucial vitamin for helping protect our bones.
Low Vitamin D levels have been linked to: other auto immune diseases (like Thyroid) plus MS and forms of Diabetes.
The main way to absorb vitamin D is via the sun (20mins at least without sun lotion) so us Coeliacs in the Northern hemispheres are often very deficient. Plus villi damage from CD means we also struggle to absorb it via the sun or from our food (eggs, fish etc). So if yours is low don't be fobbed off and follow advice to 'stay out longer in the sun'. Instead discuss with your GP for vitamin D boosters (whether injections or tablets).
For example 12 months after being strictly GF I felt like an old lady, aches and pains, tiredness, foggy headed, back spasms and fatigue. Upon visiting my GP it seemed no-one had told me that the hospital blood test I had had when diagnosed showed my vitamin D levels were extremely deficient eg 17 vs satisfactory 50 nmol/L (ideally 75+). So don't ASSUME that the Doctors all communicate superbly between hospital to GP or that your problems are just caused by 'old age'. Doctors are human and make mistakes. Plus with so many celebs having vitamin D injections as a trend it's easy for the Drs to think that people are just jumping on a Vitamin D trend.
Don't assume you're tired through being glutened. Ask about your vitamin D levels.