Hi tomatopuree ,
sorry to hear about your health problem. Having been diagnosed with a level of 7 nmol/L ( assuming you are in UK ... and using UK units of measurement ) then yes you could possibly be suffering from osteomalacia. ( adult rickets ).
The symptoms you describe would fit , however such extremely low levels of 25hydroxyD3 can, and very likely are, causing other problems for you as well.
As you probably know , vitamin D becomes a hormone in your body , it affects, directly and indirectly the regulation of 2000 or more genes. It enables your cells to read those genes and modify the behaviour of every cell in your body , from gut cells, brain cells, white blood cells , etc etc. It is for this reason that low Vitamin D can have various effects upon bodily functions.
Vitamin D exists in three states in your body , parent compound D3 (skin made - or supplement), 25hydroxyD3 ( blood storage form ) and 1,25DiHydroxyD3 , the hormone form. All three states have important physiologic functions. Your test was for 25HydroxyD3.
Your body requires all three varieties to function optimally. Vit D is the only hormone that is substrate limited and is dependant upon your behaviour , i.e. diet , sun exposure, supplementation etc. All other hormones are synthesized by your body irrespective of your actions.
In the UK , over winter sunlight is too weak to make Vit D in the skin between Mid Oct and Mid April. This is just a matter of physics. The necessary energy to make VitD is not contained in the light which does reach the earth's surface. It is UVB radiation which converts 7dehyrocholesterol in the skin , to VitD3 ( parent compound). At our latitude, 50+ degrees, UVB is absent , for 6 months of the year. It is absorbed by the longer pathlength through the atmosphere
In the summer months , UVB is present from about 11 to 3 pm. Outside these times, the sun is too low in the sky, the pathlength is longer, UVB is absorbed, however UVA is still present . IF the suns elevation is below 45 degrees ,i.e. if your shadow is longer than you , then you cannot make Vit D from that sunlight.! Again , this is simply a matter of physics.
You asked if a SAD lamp would help your VitD status. The answer is NO. Vit D is made in the skin by UVB radiation, of wavelength 312 nanometre or shorter. SAD lamps do not emit that radiation. SAD lamps emit visible light of wavelength 400 nanometre or longer. They possibly can help mood etc by stimulation of other hormones such as serotonin by acting upon receptors in the eye., which might make you feel better, so they might have a place in some treatments. Nothing to do with Vitamin D though.
Sunbeds are a different matter, SOME sunbeds emit UVB radiation , to a greater or lesser extent. So some sunbeds can make Vit D in your skin. Avoid high pressure UVA only type sunbeds they will NOT make Vit D in your skin , even though they might promote a tan. It is NEVER a good idea to burn your skin because all UV radiation can cause damage to skin , both the collagen structure ( wrinkling ) and DNA damage. The key point is to use the right sunbed responsibly, never burn or overdo it. IF you do decide to use a sunbed , It is recommended by vitamin D researchers to use a sunbed for no more than half the recommended time necessary to produce a tan , i.e. a half MED dose . A MED is Minimum Erythemal Dose, which is the dose which would cause a slight reddening of the skin by the following morning. So … never exceed half that time ! twice or three times a week may boost your vit D levels quite quickly. It is recognised that sunlight on skin can produce benefits other than Vit D production. ( See link below - * ).
Your personal circumstances of 7 nmol/L 25hydroxyD3 could lead to hypophosphataemia , arising from secondary hyperparathyroidism. Vit D deficiency can cause secondary hyperparathyroidism, it is a natural response to low vitamin D , if you consume insufficient Calcium. I am assuming that your doctor measured your calcium level and found it within the normal range ? If your calcium was outside the normal range then primary hyperparathyroidism might be suspected.as bestiswest surmised. IF your medical evaluation by your own medical professionals concluded that your Vit d level is the cause of your problems, by eliminating other causes , then in my opinion , you should try to put it right , but also understand what caused it.
Non vegetarians do consume some Vit D in animal products , a background level, depending upon how those animals were kept and indeed supplemented. Are you vegetarian? Oily fish such as salmon ( wild caught ), contains some …. Farmed salmon contain very little , just ¼ the amount of wild salmon. Do you consume oily fish ?
Vitamin D allows you to regulate the amount of calcium you absorb from your food, IF you avoid calcium containing foods such as dairy ? , then you may not absorb enough calcium. Even if you consume plenty of calcium then Low vitamin D hinders you from absorbing much calcium., leading to high parathyroid hormone , ( hyperparathryroidism) which instructs your bones to shed calcium into the bloodstream to maintain the correct i.e. normal calcium level , thus producing bone aches and pains. ( your main symptom - from reading your posts )
Another potential cause of your very low level might be malabsorption. As I indicated previously , food can contain some Vit D and its metabolites which you can utilise. IF however your digestive system does not allow that absorption , then you may develop extremely low levels, even if you are consuming animal products etc. Do you have any gut issues ? , such as gall bladder, bile insufficiency, Coeliacs, Crohn's, IBS, etc. If you do , then that may be an explanation. Vit D in food is to be found mostly in lipids ( fats ) as it is fat soluble. If for any reason you cannot digest those fats , then you may not be able to absorb the Vit D therein. It makes a great deal of sense to ask you doctor to investigate this aspect of your problem. If you find that you do have malabsorption , treatment can bypass your digestive system, from the point of view of Vit D , by either taking a daily oral spray , or using a sunbed, or indeed the sun.
I should mention that Vit d is an essential micro-nutrient , and does not work in isolation to all your other nutrient requirements. Vit D enables the nucleus of cells to read genes, which in turn create proteins in those cells, BUT , each specific cell requires all the other components to build those proteins , etc. That is you other nutrients , you need calcium, magnesium , so dark greens are very important , you need vitamin A , in many foods , you need a whole range of nutrients , so it is very important that you have a healthy balanced diet. Specifically a good variety of vegetables and some fruit. Vit D enables your cells to work with all those other components to promote a healthy body !
Probably the most important thing to consider , is what Vit d level should you achieve. There is quite a controversy at the moment. Latest research has shown that very many of us are at too low a level. Vitamin D researchers consider 100 – 150 nmol/L to be optimum. Just a few years ago in the UK , 50 was considered alright. BUT, just recently many in the medical profession regard 75 as the minimum we should now aim for. Throughout human evolution , our level was 120 -140 …. For millions of years. It is only in the last few thousand years that we migrated from Africa , where Vit D is made by strong sunlight every single day , to Northern Europe, where we cannot make it for 6 months of the year. Our body is capable of making 1000 IU in just 1 minute of sunbathing in strong sunshine , we can make 20,000 IU ,in 20 mins , at which point we naturally stop making it , until the next day . From this , it makes a lot of sense , that we do need substantial amounts for optimal health.
My advice to you would be to try and keep your vitamin D level at 100 or more permanently , make sure you get VitD3 regularly , either by supplement , sun , or maybe even sunbed. If your blood levels are below 100, your liver naturally converts your parent compound Vit D3 to , 25hydroxyD3 very rapidly , and thus reducing availability to your cells of the parent D3 , which they otherwise would use. This is just a fact of human physiology. If it turns out that you do have a digestive , or other barrier to absorption , use an oral spray , probably at least 3000 IU per day, in order to maintain those levels mentioned. When your blood level exceeds 100 nmol/L , you will start to store Vit D in your fat, allowing your body to use it , say in the case of infection , or other vitamin D resource hungry eventualities. You will be healthier !
In many cases your doctor may not want to , or may be limited in budget, so , if necessary , you can get additional postal blood spot tests from this NHS laboratory. They do charge £28 per test, if not ordered by a doctor. They will test for the general public. <a class="break-all" href="http://www.vitamindtest.org.uk/" rel="nofollow" target="_blank">www.vitamindtest.org.uk/</a> . A yearly test around end of March , early April , will give you a good idea of how you are doing.
If you do have osteomalacia , then it will take a considerable time to re-mineralise your bones , so do not stop your vitamin D treatment after 7 weeks. In my opinion you should aim to keep your level above 100 , permanently. Daily dosing is much more preferable than weekly dosing , which is again more preferable than monthly dosing. D3 has a half life in the blood stream of just 24 Hrs. 25 HydroxyD3 has a half life of about 60 days. In general your body will require 70 IU of D3 per kilogram of body weight. That is from , food, sun, supplements and sunbed , if you use it.
I have posted quite a lot here on Mumsnet about this vital question of Vitamin D deficiency, search my nick .
Also here are a few threads which explore Vit D , how people felt when low , what doses they took, how it helped etc. They are a long read , but contain lots of useful information.
www.mumsnet.com/Talk/general_health/2421492-Vitimin-D-can-it-have-this-effect
www.mumsnet.com/Talk/feeling_depressed/2868907-Vitamin-D-deficiency?pg=1
www.mumsnet.com/Talk/general_health/2841497-If-you-are-vitamin-D-deficient-what-have-you-been-prescribed?pg=1
Sorry for the length of the post …! But I hope it is useful ,
We need to keep our student nurses healthy, who knows , one day you might be treating me …! 
Best of luck . just ask me if you need any more information .
BTBH
*Benefits of sun exposure. Article in Dermato-Endocrinology.
www.tandfonline.com/doi/full/10.1080/19381980.2016.1248325
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