The most controversial nutrient at the bottom: the mystery of vitamin D

the
and
of vitamin D is probably the most debated of vitamins, and there are many mysteries to be solved about it.In the late


and early
20
th century, children in some more industrialized cities in Europe and North America generally had bone deformities and developed rickets, for example,
80 per cent
of children in London had varying degrees of rickets. In
1909
, a doctor dissected
221,
infants who had died and found that
214,
had rickets. Rickets were noticed by Greek doctors as early as ancient Rome, but never to this extent. What causes it? Some say it is because of food problems, this is evidence, when some doctors found that if patients with rickets take cod liver oil, can cure rickets, they think that grease played a role. Some people think that rickets are caused by the harsh living environment, such as

fog
"
London air pollution is serious, no sunlight. They pointed out that poor tropical countries have worse food and sanitation conditions than the United Kingdom, but rickets are rare, it can be seen that adequate sun exposure can prevent rickets, can be prevented and treated by sun exposure.1919,
, The British doctor Edward
.
melanby used animal experiments to systematically study the causes of rickets for the first time. Vitamins

,
B1
and
C
have been found, and will rickets be caused by a lack of one of these vitamins? Melanby's feeding of vitamin
B1
-rich yeast or vitamin
C
-rich orange juice to rickets was ineffective, but feeding vitamin
A
-rich cod liver oil, butter or milk could prevent rickets. According to Melanby, rickets are caused either by a lack of vitamin
A
or by a lack of something similar

vitamin
A.
1922,
, the American biochemist

A was found to be
.
McCollum repeated Melanby's experiment with mice. McCoole knew that if fish liver oil was oxidized, vitamin
A
would fail and no longer have the effect of preventing vitamin
A
deficiency, but he found that oxidized fish liver oil could still prevent rickets in mice, proving that fish liver oil contains a new vitamin, the
4
vitamin found, so it is called vitamin
D
.so why can sunbathing also prevent rickets?
1925
German chemist Adolf
.
has shown that cholesterol in the skin can be converted into vitamins when exposed to sunlight
D
, the mystery is solved.
three
, Windus won the Nobel Prize. But this transformational process was

in 1973. We now know that ultraviolet light in sunlight converts
7-
dehydrogenated cholesterol from the skin into bile osteosterol (vitamin
D3
), which is sent from the blood to the liver, where it is converted into osteotisol, which is then converted into osteotisol in the kidneys. Osteosterol binds to vitamin
D
, which controls the absorption of calcium from the small intestine and maintains a balance of calcium and phosphorus in the blood, making it essential for bone health.not only humans, but other animals can synthesize vitamin
D
themselves, including feathered birds and long-haired mammals. You may find it strange that feathers and hair block sunlight, and how does the skin synthesize vitamins
D
? These animals secrete fat on feathers and hairs, and the cholesterol in the fat produces vitamin
D
under the action of sunlight, and then they eat vitamin
D
by combing their feathers and hair. Man's ancestors, known asNaked Ape " and living in sunny tropical Africa, did not have to worry about vitamin
D
deficiency. Vitamin
D
deficiency is a serious threat when humans migrate to the less sunny north, and under the effect of natural selection, the skin tone of the northern population gradually becomes lighter so that they can fully absorb the sun to synthesize vitamin
D
. By the time humans get dressed,
vitamin
D deficiency becomes a threat again.since humans are able to synthesize vitamins
D
, strictly speaking it is not a vitamin. But this synthesis requires the participation of sunlight and is limited to ultraviolet light (
UVB
) in a particular band of sunlight, which cannot be synthesized if the sun is coming through glass or sunscreen is used. If you don't use sunscreen to get in the sun, you're at increased risk of skin cancer. Therefore, the medical profession does not recommend the prevention of vitamin
D
deficiency by sun exposure, but vitamin
D
as a true vitamin, supplemented by diet. So how many vitamins should you take
D
day? The Original recommendation of the American Academy of Medical Sciences was to supplement
200
IU (
IU
, equivalent to
5
micrograms) of vitamin
D per day, starting in infants

, double


400 IU
) until
50,
, and


600 IU
.
2011
the American Academy of Medical Sciences raised the standard to
0
to
400 IU per day for infants between
and
month
s
.
1

70
years old supplement
600 IU
,
71
years old to supplement
800 IU
. Vitamin
D
is rich in a small variety of foods, only fat fish, full-fat milk, eggs, certain types of mushrooms, etc. , insurance practice is to eat vitamin
D
fortified foods and oral vitamin
D
Agents, especially breastfed infants, because breast milk is almost free of vitamin
D
, be sure to supplement vitamin
D
preparation (formula has been added vitamin
D
, no need to supplement).even so, many biomedical experts have criticized the American Academy of Medical Sciences for

recommended vitamin
D intake too low. This intake is sufficient to prevent rickets and cartilage in adults, but is it sufficient to maintain bone health? Vitamin
D
not only vital to bone health, but also plays an important role in immunization, so does this intake help prevent chronic diseases? Many believe that high doses of vitamin
D
can prevent osteoporosis, cancer, cardiovascular disease, multiple sclerosis and other diseases, but the results of clinical trials are not yet accurate and controversial. One of the more accepted conclusions is that older people who take
700
to
1000 IU
Vitamin
D
daily have a lower risk of falling than oral placebo.vitamin
D
is a fat-soluble vitamin, if you take too much from the diet, will accumulate in the body, can lead to excessive blood calcium and other adverse reactions. If the human body synthesizes vitamin
D
itself is not concerned about this, because once vitamin
D
is synthesized too much, the body will destroy it, do not worry about because of too much sun exposure to vitamin
D
poisoning. However, there is a risk of vitamin D from
especially
preparations. So what
limit
vitamin D intake should be? The original ceiling set by the American Academy of Medical Sciences was
0
to

12 months for infants
1000 IU
,
1
years old for
2000 IU
, later changed to
0
to

6
1000 IU
6

12
months
1500 IU
,
1
to
3
years old
2000 IU
,
4
to
8
years old
3000 IU
,
9
years old
4000 IU
. But biomedical experts have criticized the limit as too low, arguing that the risk is not until
10,000 IU
, and that the American Endocrinology Association's cap for adults is
10,000 IU
. The
and
of vitamin D is probably the most debated of vitamins, and there are many mysteries to be solved about it.