Vitamin D is not produced under any cloth (like Hijab)
DIRECT sun rays upon the bare skin are needed in order to produce vitamin D. Therefore, our body produces no vitamin D behind any cloth (like Hijab) or behind any glass window. Even if we have the hottest sun in the Arab desert with over 50 degrees Celsius temperature, but no vitamin D is going to be produced under the Hijab (link).
Thus, according to all scientific studies, Arab women suffer the highest rate of vitamin D deficiency in the world.
But Muslim behaviour is unfortunate.
They deny any role of the Hijab in vitamin D deficiency and start bringing up lame excuses like vitamin D deficiency could also occur due to obesity, race or if you have some special diseases like malabsorption of nutrients from food etc.
But a scientific study, which has been done in Istanbul, Turkey, brought all their misinformation to an end. In that study, women of the same race, from the same region were studied. Half of them wore the Hijab, while half didn't. And the results showed that half of the women with Hijab had a huge vitamin D deficiency as compared to the half that didn't wear Hijab. The prevalence of vitamin D deficiencies was 55.0% for covered and 20.0% for uncovered women. Link to Istanbul Study.
You are hurting your baby girls by confining them into Hijab
Istanbul study (link) also found out that vitamin D deficiency is not only associated with clothing styles like Hijab but also with the age at which a female begins wearing Muslim-style clothing.
Your baby girl is especially in danger of vitamin D deficiency if she is confined into Hijab at an early age.
If you are a Muslim mother (or father) of a baby girl, then fight back against your family and Islamic society for the sake of your baby, and don't let them push you to confine your baby into Hijab. Let your baby girl play freely and become healthy and happy.
Vitamin D supplements are not as good as natural sun-rays
Muslims come up with their next lame excuse, i.e. no problem with Hijab as women/girls could take the vitamin D supplements.
But the scientific studies (link) show that Sunlight-exposure has a more positive effect on bone structure and homeostasis than vitamin D supplementation and control. The sun-exposed vitamin D deficient group showed a significant reduction of parathyroid hormone more than that in the vitamin D supplemented group vs. VDD controls (67.69 ± 13.18 and 78.93 ± 8.31 vs. 86.05 ± 9.67 pg/ml, respectively).
Allah is still guilty of vitamin D deficiency in the women of the last 1400 years and those poor women who cannot afford to buy supplements
Muslim excuse of "Vitamin D supplement" still does not make Allah free of being guilty.
Vitamin D supplements started only a couple of decades ago, but what about the Muslim women of the last 1400 centuries, who suffered vitamin D deficiency (and thus a lot of diseases) due to the Hijab? Allah confined them into Hijab and also into the 4 walls of their houses.
Therefore, if Allah really exists, then he is guilty. And if there exists no Allah, and all this revelation was a human drama of Muhammad himself, then Muhammad is guilty of all these sufferings of Muslim women.
In simple words, this vitamin D issue proves that there is no all-knowing and most Wise Allah present in the heavens above. And since Muhammad was neither all-knowing nor all-wise, thus his ignorance became the cause of vitamin D deficiency among billions of Muslim women of the last 14 centuries.