Everyone seems to agree
that vitamin D is important throughout life. This is certainly as true in the
first year of life as it is later on. For it is during the first year that, in
addition to its role in calcium metabolism, this critical nutrient reduces both
the risk of current infections and the late-life development of such autoimmune
diseases as multiple sclerosis and type 1 diabetes. Both the Institute of
Medicine (IOM) and the American Academy of Pediatrics (AAP) agree that vitamin
D intake during the first year of life should be 400 IU/d. My own estimation of
the requirement (for different ages and body sizes) is 65–75 IU/kg body weight
per day. For average body weights in infants during the first year of life that
rule of thumb computes to somewhere between 300 and 500 IU/d for infants. So,
while there is still contention with respect to the optimal intake for adults,
there really is no disagreement about how much is needed for infants, either
among various authoritative sources or arising from different approaches to the
evidence. With respect to infants, 400 IU/d seems to be just about right.
The question is, how is
the infant to get that vitamin D? Human milk, in most nursing mothers, contains
very little vitamin D. Infant formulas, from various manufacturers, all contain
some added vitamin D in amounts calculated to be sufficient to meet an infant’s
needs. But extensive studies during the first year of life reveal that less
than one-fifth of all infants ever get as much as the recommended 400 IU/d from
any source, and fewer than one out of 10 breast-fed infants meet the
requirement. As a result, the AAP urges that all infants, regardless of whether
they are breast or formula fed, receive their 400 IU/d as pediatric drops.
Unfortunately, this recommendation, while appropriate, is not often followed.
Most babies are just not getting the vitamin D they need. The late-life
consequences of this shortfall could be enormous.
It must seem strange that
on the one hand we stress that human milk is the best source of nourishment for
our babies, and on the other seem to ignore the fact that human milk doesn’t
contain the vitamin D those babies need. The explanation, very simply, is that
the disconnect is artificial. Nursing mothers have so little vitamin D in their
own bodies that there is little or none left over to put into their milk. But
it has not always been this way. We know that the vitamin D blood
concentrations that are regularly found today in Africans living ancestral
lifestyles are high enough to support putting into breast milk all the vitamin
D an infant needs. But the bulk of the world’s population today is not living
on the high equatorial plains of East Africa nor exposing much of its skin for
most of the day.
Fortunately, we don’t have
to return to East Africa. It turns out that, if we give nursing mothers enough
vitamin D to bring their blood levels up to the likely ancestral levels, then
they automatically put all of the vitamin D their baby needs into their own
milk, thereby ensuring that the infant gets total nutrition without the need to
resort to vitamin D drops.
How much vitamin D does
the mother need so as to ensure an adequate amount in her milk? As with
everything else related to vitamin D, there is a lot of individual variation,
but it appears that the daily intake must be in the range of 5,000–6,000 IUs.
As no surprise, that’s just about the amount needed to reproduce the vitamin D
blood levels in persons living ancestral lifestyles today. And while
5,000–6,000 IU may initially seem high, it is important to remember how much
the sun produces for us. A single 15 minute whole body exposure to sun at
mid-day in summer produces well over 10,000 IU.
There is one important
proviso for nursing mothers concerning the needed intake. Those who live in
North America and have to rely on supplements should be certain that they take
their supplements every day. While for other purposes it is possible to take
vitamin D intermittently (e.g., once a week), that doesn’t work for putting
vitamin D into human milk. The residence time of vitamin D in the blood is so
short that, if the mother stops taking her vitamin D supplement for a day or
two, vitamin D in her milk will be low (or absent altogether) on the days she
skips.
There is a glaring
disconnect here between these well-attested physiological facts and the
official IOM recommendation for nursing mothers, i.e., only 400 IU/d – the same
intake for her as IOM recommends for her baby (whose body weight is less than
10% of her own). The IOM, if it were to be explicit about its current
recommendations, would be telling nursing mothers something like this:
“The evidence we analyzed
indicates that your own body needs only 400 IU of vitamin D each day.
Unfortunately, that won’t allow you to put any vitamin D into your breast milk.
Sorry about that . . . So, if you want to ensure that your baby is adequately
nourished, you are going to have to resort to giving your infant vitamin D
drops.”
That would be a hard
message to sell, and clearly, it makes little sense on its face. As I have
already noted, women living ancestral lifestyles (whether or not they are
nursing an infant) have far higher blood levels of vitamin D than contemporary
urban Americans. Milk production (and its optimal composition) are simply two
of the many functions that vitamin D supports in a healthy adult. This
breast-feeding example is not a special case; it is just one of the many pieces
of evidence that point to the fact that current vitamin D recommendations for
adults are too low – way too low.
Vitamin D supplements –
and in this case vitamin D drops – are literal lifesavers for infants today.
But what about two or three generations back – before nutritional supplements
come into existence, but long after migration out of Africa? Ninety years ago vitamin
D had not yet been discovered, and there certainly were no vitamin D
supplements that could have been used. How did we get by through those
thousands of years? There are two answers. Most of us, living in temperate
latitudes, got a lot more sun exposure than we do today, and of course there
were no sunscreens, so there was no blocking of the solar radiation that
produces vitamin D in our skin. Those of us living in far northern latitudes
survived mostly by depending upon diets that were very high in seafood, which
is naturally a rich source of vitamin D. And those of us who got vitamin D by
neither route were at increased risk of a whole host of vitamin D-related
disorders, most obvious and most easily recognized being rickets.
The bony deformities of
rickets were common a century ago in Europe, North America, and East Asia, and
were largely eradicated in growing children by use of cod liver oil and, in the
US, by the introduction of vitamin D fortification of milk in the 1930s.
Fortunately, growing children can repair some of the bone deformities of
rickets if they are given vitamin D soon enough. But, repairing rickets, while
a good and necessary thing to do, is not sufficient. It is too late, by the
time we recognize the deformities of rickets, to ensure maximal protection
against the autoimmune diseases (for example), for which susceptibility is
mainly determined in the first year of life.
To sum up, we now better
recognize the importance of vitamin D in the earliest stages of life.
Furthermore, there is, as noted earlier, quite good agreement on how much an
infant needs. Where we lack consensus is how to make certain that all of our
babies get the amount they need. Why not rely on giving nursing infants vitamin
D drops, as the AAP recommends? Two reasons: 1) It’s been tried and has failed;
and, 2) When it does work in individual infants, it provides no benefit for the
mother. By contrast, ensuring an adequate vitamin D input to the mother during
pregnancy and lactation is almost certainly the best way to meet the needs of
both individuals.
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