| |
Vitamin D - A Symphony of Enigma Variations
The key for harmonious sunny delight
L’Attitude
Do you turn your coloreds inside out when you hang them on
the line outside to dry? Probably not if, like VEGA, you dwell
and work in the UK, somewhere between latitudes 50º and
60º N, because the sun’s actinic rays are not powerful
enough, even on a clear day, to bleach or fade the dyes. Bessie
Chu, who has worked with VEGA and educated us a lot, hails
from Wuhan, up the Yangtze, and Shanghai, and has therefore
lived at latitudes around 30ºN, takes it for granted
that the coloreds have to be aired outside inside out.
Most of China lies south of the 50º line. Paris, 5º
south of London, also lies south of 50º N. Birmingham
and Moscow lie at about 55ºN, and in the Antipodes navigators
clearing Cape Horn must reckon on courses set at about 55ºS.
Many centres of population lie on or near 40º latitudes:
New York, Beijing, and Wellington (New Zealand North Island),
for instance.
The Indian sub-continent spans latitudes between 25ºN
for Kashmir to Colombo in Sri Lanka and the Maldive Islands
only a few degrees north of the equator. This span is literally
heightened by the range of altitudes. Australia covers latitudes
from 10º to 40º S and represents a good example
of the effects of travel, migration, and genetics that have
generated vigorous policies to counter adverse manifestations
of harm from sunshine in the form of damage to the skin. Premature
wrinkling and cancer, attracting an industry of sun blocks
and protective clothing, bear witness to this concern.
The Body of Evidence
Early nutritional research in the first half of the last
century, in the heyday of discoveries of essential factors,
associated the skeletal disorders attributed to deficiencies
(and excesses) in lifestyle to factors, as with other vitamins,
in the diet. Much of this research was conducted in the rich
countries of the West with impoverished ghettos of undernourished
communities living in high latitudes and under the polluted
skies of the Industrial Revolution, which the rays from the
sun barely penetrated. Pallor ruled. Animals, birds, and fish
were less afflicted, so foods and offals derived from them
were dietary sources of the antirachitic factors. The era
of cod and halibut liver oils was established, although some
young children were stripped and lined up in hospitals for
exposure to ultraviolet lamps in an atmosphere that smelt
of ozone; at least goggles were provided. Such risky procedures
would not be permitted now; sunbeds in luxurious environments
have latterly fallen out of favor as a quick way of acquiring
a tanned torso. For millions of the rickety children of the
advanced nations, the ordeals of codliver oil reigned—and
in Britain fish was cheap, and unclean emissions into the
atmosphere went unpenalized. There was no danger of the coloreds
coming off the line faded; more likely they would dry dingy
and the whites would be smutty.
Deception
In the first enigma of vitamin D we must accept that it maskerades
as a vitamin: unlike their dependence on the vitamins such
as C and B, human beings can survive in many circumstances
without a dietary source of vitamin D. It is an essential
factor, and we have to assess, particularly where the adequacy
of sunshine is in doubt, the significance of dietary sources.
Red-headed, blue-eyed, fair-skinned “Celts” represent
one species with sensitivities that keep them out of the sun—if
not out of the limelight, for examples are prominent in European
affairs, notably in the more northerly latitudes and thus,
in the British Isles, in Scotland and northern Ireland. Is
it any wonder that in maritime affairs the Scottish influence
was noted more in the engine-room than on the bridge?
Geneticists postulate that the first human redheads walked
this earth as Neanderthals about 50,000 years ago and then
spread into northern Europe, where they concentrated, as now
seems fitting for their comfort and survival, at the higher
latitudes. A single abnormal gene mutation, which controls
formation of the melanocortin-1 receptor, is responsible for
the red hair. This gene is carried by about 40% of present-day
Scots; high levels of breeding between red-heads and dark-skinned
people in Scotland buried the abnormality in the genome, but
left an association between color of the skin and its sensitivity
to the sunlight. This predisposition has spread in diluted
forms more widely and the significance of dietary sources
has increased accordingly, although in many instances imperceptibly,
because migrants into higher latitudes have exploited the
ability of other species to synthesize vitamin D in edible
forms in which even the fairest-skinned carriers of the “Celtic
abnormality” may indulge, possibly to excess: disasters
of exploratory missions in the icy wastes have been attributed
to “life-saving” consumption of livers from slaughtered
polar bears. The excess of fat-soluble vitamins and iron was
enough to finish off the unwary explorers, their intake being
unbalanced by the lack of fresh food and sources of anti-oxidant
substances.
Dependence
Carriers of the disabled gene benefited from a mutation with
value-added attraction. Not only did the abnormality survive
the cull that carried off two-thirds of the European population
in the Black Death — a bacterially-transmitted plague
of comparable significance to today’s HIV and to the
gloomiest predictions of BSE-derived CJD—but redheads
acquired attributes of beauty and of being good stock to breed
from. With displays of rufous beards men could add to the
protection and concealment of their skin, while adding a further
putative embellishment.
The Beatitudes omitted the blessedness of redness, and the
attractiveness of the countenance. Ancient Egyptian, Assyrian,
Persian, and Byzantine women won male approval by dipping
their wigs in henna. Men would dye their beards to match.
This was a genetic modification to dye for. “None but
the brave deserves the fair.”
By Shakespeare’s time, however, red hair had become associated
with liars and witches: Rosalind in As You Like It has “hair
of a dissembling color.” On the other head, Queen Elizabeth
I preferred to cover her own bald patches with rouged wigs;
by the 1800s red hair was firmly regarded as a mark of the
harlot and “ladies of poor character.” Pre-Raphaelite
artists, such as Rossetti and Burne-Jones, displayed a preference
for redheads and the auburn-haired, and the trend for fashion
and beauty continued to the end  of
the century. The Celtic countenance inspired artists such
as Degas, Renoir, Toulouse-Lautrec, and Klimt.
Latterly Rita Hayworth, Lucille Ball, and Ginger Rogers have
exemplified both countenance and body beautiful. With the
physical and sexual attraction, especially in women, of victims
of sun-avoidance goes a reputation as butts of derogatory
banter. Robin Cook, until recently the Foreign Secretary,
and Chris Evans are representatives of today’s clan of
people who owe most to the the animal kingdom and the skill
of the chemist to survive and perform unmutilated by the toll
of skeletal and other defects associated with vitamin deficiency.
Dilemma and Deficiency
Dark skins, migration, religion, and politics comprise another
twist in the story of vitamin D. Developments in colonial
Africa drew in immigrants from southern Asia as workers, many
of whom prospered until they had to leave hurriedly under
threat of oppression. They migrated to their passport home
in the cold northern latitudes of Britain, where they joined
other populations of dark-skinned immigrants arriving after
WW2 and, as most incomers begin, settling in poorer city areas
where already stretched social and medical services failed
to cope with the added difficulties of language and communication.
Rickets, common after WW1 but essentially overcome by the
end of WW2, recurred seriously in the new populations, whose
dark skins (thanks to genetic selection for protective supplies
of melanin in the skin) had acclimatized them for a much higher
intensity of sunlight than they would experience in the environs
of Britain’s poorer areas. Moreover, their habits and
diets, combined with genetics, told against them: immigrants
of a Hindu persuasion ate little meat and offals, and Muslims,
particularly the women and children, covered themselves religiously
correctly but physically imprudently, and they were home-bound.
Milk in Britain’s mother cows comes from animals kept
indoors for half the year and they too have to manage with
the vagaries of the summer weather; accordingly, summer milk
and its derivatives (such as butter, ghee, and buttermilk)
were—and are—only a modest source of the sunshine
vitamin, and winter milk is poorer still. Low-fat commodities
may be depleted by loss of some of the already meagre content
of vitamin D into the cream. Labels do not tell all; and,
anyway, the devil is in the detail in minute print or obscured
by stick-on information and advertising.
Britain, unlike other industrialized countries, has not fortified
the “pure, white, and natural” with vitamin D. This
omission appears to represent a curious reluctance to “muck
about with” or “adulterate” a product derived
from a mess of mucky contaminations and tainted with the ills
of tuberculosis, brucellosis, and other bacterial food-borne
hazards. Resistance to pasteurization persists to this day.
The unnatural alternative margarines* and yellow fats and
spreads (as well as some derivatives, such as yogurts, of
animal milks) are actually better sources of vitamin D (and
A), because they are fortified. Plant-milks of many brands
are fortified likewise. VEGA maintains its pressure on manufacturers
of alternatives to dairy-produce (which are understood to
be more than fun foods) to fortify their products accordingly—or
at least to declare deficits. VEGA seeks support from the
Food Standards Agency on this.
*Margarine, like butter, describes a yellow fat comprising
at least 80% fat, the rest being almost entirely water. Unlike
butter, margarine is required by law to be fortified with
vitamins A and D. Spreading fats with a lower fat : water
ratio are so fortified by voluntary agreements in the trade.
“Vegetarian” margarine used in the baking trade
and disclosed among the ingredients listed on labels on products
such as cakes and biscuits, with claims of suitability for
vegetarians/vegans, is likely to contain whey, a by-product
of cheese-making. Additives and enhancements such as omega-3
or DHA sources introduce specific fatty acids derived from
microalgae by processes of biotechnology.
Rickets, a juvenile form of osteomalacia or osteopenia that
arises in several genetically differentiated forms, afflicts
people in tropical and sub-tropical areas where diets are
deficient or where women’s bodies are heavily obscured
by clothing, usually according to religious practice. The
disease can lead to irreversible stunting and, as a result
in young women, difficulties in child-birth. The harm in the
form of osteoporosis in the elderly now affronts many societies,
especially where women have good chances of survival postmenopausally.
The price of modesty among followers of Islam, haredi (ultra-orthodox)
Jews, and the Bedouin in sub-tropical lands may be paid in
the currency of skeletal deformities.
Some people may suffer from the added embarrassment of phototoxicity
in which their skin erupts in an exaggerated fashion into
wheals and rashes owing to the consumption of certain vegetables
containing substances called psoralens or of drugs such as
the antibiotic tetracycline. Contact of the leaves of certain
plants, eg parsely, carrots, and parsnips with bare skin under
bright sunlight brings out rashes associated with the cultivation
and sale of vegetables; hikers will recognize the problem
when they brush bare-legged through vegetation in which the
leaves of notorious immigrants such as the giant hogweed have
generated the full complement of phototoxicants. Such deterrents,
added to allergies such as hay-fever, deny many people the
sunny delights of summer. However, some people benefit from
developments of these observations: rigorous treatments—so
called PUVA therapy—claim remissions of psoriasis for
patients administered psoralens and irradiated with ultraviolet
light under strictly controlled conditions.
Depression
Fish and chips (probably cooked in beef tallow) and, possibly,
mushy peas—and, of course, vinegar– spared Britain
severe outbreaks of “Third World deficiency diseases”
during the years of Depression after WW1. These cheap home-produced
staples, eked out with milk (in areas of London cows were
walked round for milking to order in the street) and provender
from allotments and a pig or a few poultry, sustained a Lowry
population toiling under the polluted skies of those dark,
satanic mills, even at the cost of longer-term consequences
we may rue in the better conditions of today. At the end of
the 19th century civil servants had already remarked on the
poor stature of the intake of recruits to fight the Boer War.
At the end of WW1, after a terrible toll of the nation’s
best male breeding stock —at least physically –
Britain’s Prime Minister surveyed Homes Fit for Heroes
with the prescient lament: How can we build an A1 Empire with
a C3 Nation? An era of social revolution, farming and food
policy, and physiological and nutritional discovery was quickening.
Discovery
Inklings of the association of the benefits of sunshine and
what we recognize now as vitamin D go back to antiquity. Rickets
as a disease was described scientifically about 1650, but
the association with diet was stumbled on in 1920 by Sir Edward
Mellanby, who was experimenting on dogs kept indoors with
the exclusion of sunlight or UV light and devising dietary
regimens. He clinched the association of rickets with a deficiency
of a food factor that in the knowledge of the time could be
ranked as a vitamin; further, he established that the factor
was fat-soluble and that cod liver oil was an effective antirachitic
agent.
A few years later the fat-soluble vitamin was distinguished
from vitamin A, and illumination with sunlight or UV of a
steroid (7-dehydrocholesterol) in skin yielded a substance
that prevented rickets in otherwise deprived rats. Irradiated
rat food protected the animals similarly. The interpretation
that “light equals vitamin D” technically removed
the strict definition of the factor as a vitamin.
By the end of the 1930s German scientists had identified
compounds and their congeners and had reproduced the conversions
of the secosteroids on exposure to UV light that generate
the vitamins —now plural because at least 2 series were
identified, vitamin D2 resulting from the irradiation of ergosterol
obtained from yeast, and vitamin D3 deriving from the dehydrocholesterol
precursor. Sources of vitamin D manufactured as a food additive
or supplement remain yeast for D2 and wool-wax (lanolin) for
D3. The vitamin is declared on many food products unnumbered,
an omission vexing to some veggies rigorous in their purchases,
and convenient for those “not wishing to be bothered
with all that.”
To veggies who refuse any woollen products, the difference
is significant, and they should support manufacturers who
declare additions of vitamin D2. Sheep are reared in various
parts of the world for different markets, e.g. meaty Suffolk
crosses in the UK and woolly, hardy merinos in the Antipodes.
Sheep normally moult seasonally, and in lands such as northern
Europe, to which many breeds are not acclimatized, shearing
in early summer can be beneficial; it may also be done to
save space when sheep are intensively penned, marketed, transported,
or prepared for lambing. That said, the hard work of shearing,
paid at headage rates, is not a gentle job, especially when
the return on wool is poor (much of it is too coarse for finer
clothing, but is suitable for carpets), so veggies have grounds
to keep commercial wool and its derivatives out of their purchases.
Some wool (and certainly sheepskin) will come from animals
flayed in the slaughterhouse, possibly killed by ritual (i.e.
Jewish or Muslim) procedures.
D 4 2 or 3 4 D?
D2 or D3, there is another complication, which engages VEGA
and manufacturers in Europe and North America. Vitamins, flavorings and other substances
may be added in the form of microencapsulated beads; the capsule
may be made of gelatine. What with BSE and other problems,
pig-gelatine is preferred by the trade for this purpose —
and VEGA has even heard of a fish-derived product sold as
vegetarian gelatine. Encapsulation can, however, be achieved
without resort to animal-derived products.
SPOT THE DIFFERENCE!
The Structure of Vitamin D2 and D3
 In
the arithmetic two does not equal three in several respects.
Vitamin D3 is much the more active form for some species,
notably poultry, and demands for supplementation are heaviest
for the millions of animals housed in intensive farming systems.
Vitamin D3 and its derivatives serve human and veterinary
purposes the best, and they comprise most of the vitamin D
in commerce. In people the physiological effects of D2 and
D3 have been reckoned to be equal, but in some respects the
D2 series may have only half the potency of the corresponding
D3 compounds.
Consistent veggies will not want to become accomplices to
any activities of the sheep industry, so their rejections
of products containing vitamin D3 (or just vitamin D) are
well versed (and, even better, as part of VEGA’s consumer
campaign, described forthrightly in communications to manufacturers
and retailers, for a dwindling demand for D2 may see an end
to its production).
Birds derive vitamin D3 by preening, exposure to the sun
having transformed compounds of the essential water-repellent
oils on the feathers.
Nutritional needs must when the devil of unavailability drives.
Deficiencies of vitamin D and other nutrients are serious,
and avoidances for some reasons may have to be overridden
by others even more important but still unresolved. Veggies
should ensure that they and theirs get plenty of exercise
and exposure outside and prudently reduce the need for supplements
containing vitamin D; if they have recourse, even so, to a
supplement, they should insist on vitamin D2 (ergocalicferol).
For some medical purposes, however, only D3 forms are available.
Physicists and biochemists offered nutritionists in the 1960s
a splendid new research tool with isotopically labelled versions
of vitamin D and related steroidal compounds. As a result
another reason arose to withdraw the vitamin designation:
the substances produced in the skin and taken in the diet
or in supplements are pro-hormones for some messenger functions
on various organs of the body, according to the competence
of receptors distributed at various sites, not just in the
bones.
This research ran at a still faster rate when pharmacologists
and geneticists began to work out the metabolism of drugs
and the detoxification of apparently dangerous compounds (and,
in some instances, the reverse). VEGA was involved, in an
earlier incarnation, in tests to determine such differences
in the liver function of native veggies and veggies of southern
Asian origin, in the belief that more than skin color was
involved in the predisposition to rickets. This small study
has been overtaken by others in greater detail, reinforcing
this belief.
 The
pro-hormone vitamin D has to undergo two steps before it becomes
fully active endocrinologically (see diagram below). These
are enzymically-controlled hydroxylations by specific P450
agents concentrated in the liver and in the kidney. In the
first pass the precursors circulate in the blood to the liver,
where they are hydroxylated to 25(OH)D3 (we illustrate here
only the D3 series), which is the major form of the pro-hormone
in circulation and usually the means by which vitamin status
can be measured. The kidney next functions as an endocrine
gland to produce two principle dihydroxylated metabolites
1a,25(OH)2D3 and 24R,25(OH)2D3, which are transported to target
sites for binding at a nuclear receptor and, in hormone mode,
to elicit the appropriate biological responses. Operation
of this endocrine system depends on a binding protein in the
plasma that carries the pro-hormone and metabolites to the
appropriate receptors for biological activity. It follows
that malfunctioning of the liver or kidney can induce symptoms
of vitamin D deficiency; synthetic versions of the active
metabolites are available to circumvent such a block.
Vitamin D in its active form is a steroidal hormone to be
rated with aldosterone, cortisone, estrogens, progestins,
and testosterone, and is implicated with many other factors
in sites of receptive cells in organs other than liver, kidney,
blood, and bone: in the parathyroid and thyroid glands, for
instance, and in the pancreas, skin, lung and intestine. It
is a strong player in the endocrine orchestra, in which it
should contribute harmoniously with the other hormonal instruments
and with vitamins C and K and inorganic factors such as calcium,
phosphate, and fluoride.
Regulation of the hydroxylating enzymes tunes circulating
levels of the hormone to intakes of calcium, phosphate, and
proteins and with the output of parathyroid hormone; in bone
formation calcitonin, a polypeptide hormone generated in the
thyroid gland, is also important. Supplementation with calcium
may be ineffective or even harmful unless balanced by additions
of vitamin D; dietary intakes too rich in protein, especially
derived from meat and fish, may induce urinary losses of phosphate
that lead to some forms of osteopenia (such as osteoporosis).
Carriage of vitamin D and its metabolites to their target
organs is under the control of the plasma vitamin D binding
protein VDR. Blood tests give powerful evidence of vitamin
D status and of specific disorders and the need for focussed
medical treatment. Recent research, mainly on animals, has
raised hopes that vitamin D in its various forms can be applied
in treating autoimmune diseases such as multiple sclerosis
and rheumatoid arthritis and in suppressing rejections of
organ transplants.
Various snippets of evidence illustrate surmises on the genetics,
effects of latitude and migration, and involvement of vitamin
D and possible means of treatments, e.g. in bone disorders
in Crohn’s disease and for Gujerati Indians who have
moved from Africa to live in affluent areas of London: they
are 3 times likelier to develop symptoms of tuberculosis than
those who had stayed put, and impairment of their vitamin
D status is implicated. A Viking gene predisposing to circulatory
problems is surmised to explain pockets of greater risk in
once-invaded areas of England and Scotland, worsened in northerly
areas and in places of disadvantage where osteomalacia (e.g.
rickets) is also likely to be commoner.
The nearer to the Equator, the lower the risk of heart disease
runs one axiom. Evidence is quite strong for a latitudinal
association with increased risk of dying of cancer of breast,
colon, prostate, and ovary. Black men, who are prone to deficiency
of vitamin D, have an elevated risk over white men of prostate
cancer and of a more aggressive form of the disease.
Mad Dogs and Englishmen
Terrestrial organisms have been producing sunlight-mediated
vitamin D for over 300 million years. As vertebrates evolved
from their calcium-enriched ocean environment for terra firma
they depended on the cutaneous synthesis of vitamin D for
raising the efficiency of intestinal absorption of scarce
sources of dietary calcium. Exposure to sunlight has been
the most important agency in maintaining vitamin D status;
the adverse effects of industrialization, migrations, poverty,
and religious practices have been augmented sharply by the
fear of skin cancers, use of sunblocks, and inadequate compensatory
fortification of diets. Seasonal variations and cloudiness
emphasize the significance of latitude (and altitude).
With adequate exposure to sunlight, dietary additions of
vitamin D are unnecessary. However, the variables in lifestyle
and exposure necessitate the fortification of foods, especially
for populations in northern Europe (where, for instance, and
in contrast with the USA and many countries, fortification
of dairy-produce and some alternatives is inadequate - see
our Case Studies page for an example of rickets in a child
fed unfortified plant milk). Nutritionists apply fortification
cautiously, because hefty additions after WW2 to some baby-foods
led to serious damage to the infants’ kidneys.
Dosage
As a rough guide dietary intakes of vitamin D are recommended
at 200 IU (5 mcg) a day for people up to the age of 50, doubled
for people from 51 to 70, and trebled (i.e. to 600 IU = 15
mcg) a day for people older than 70 years. For pregnant and
lactating women the recommended dietary allowance is 200 IU
(5 mcg) daily. Certain animal products in the UK are commonly-available
unfortified sources of vitamin D3, especially salt-water fish
(such as herring, salmon, sardines, and fish liver oils);
milk, eggs, veal, beef, and butter provide small amounts.
Plants, fruits and nuts are negligible sources, but an increasing
array of fortified foods (e.g. breakfast cereals, spreading
fats and soya products) are suitable for veggies, with labels
detailing contents.
Professor Michael Holick of Boston University Medical School,
USA, has calculated some levels of exposure relevant to areas
at about 40º latitude. Exposure of the body in a bathing
suit to 1 minimal erythemal dose (MED) of sunlight (enough
to redden the skin) is equivalent to ingesting 10,000 IU of
vitamin D; therefore a daily intake would be met by 1 MED
of about 6 to 10% of the body surface. Exposure of hands,
arms, and face 2 or 3 times a week to a third to a half of
an MED (i.e. about 5 minutes in Boston at noon in July) in
spring, summer, and autumn is more than adequate. Excessive
exposure to sunlight cannot induce vitamin D intoxication;
anyone wishing to stay outside longer than so recommended
should apply a sunscreen with a protection factor of at least
15 to prevent sunburn and damaging effects of excessive exposure.
To guarantee vitamin D sufficiency for the house-bound (e.g.
residents in nursing homes) a dose of 50,000 IU could be offered
once a month; to reverse deficiency, offer 50,000 IU of the
vitamin once a week for 8 weeks. “It is remarkable how
exposure to sunlight a few times a week can reduce the risk
of osteoporosis, osteomalacia, muscle weakness, fractures,
and maybe some of the common cancers, but also induce a feeling
of wellbeing,” states Professor Holick (Lancet, 6 January
2001). Evidence from an experiment on submariners indicates
a benefit from sunlight to the bodily biochemistry over and
above dietary adequacy in vitamin D.
Some lipid-lowering drugs, such as cholestyramine, impair
absorption of vitamin D in the intestine and thus increase
the danger of fractures due to osteomalacia.
VEGA draws attention to the weaker UV radiation effect in
the latitudes of the British Isles and to the use of international
units, which reflects biological tests on animals (mainly
rats) in original methods of measurement, now mostly succeeded
by “black box” analysis based on physical chemistry.
Dogma Doubly Dented
The vitamin D variations have two more enigmas to solve.
Vitamin D has been classified in popular nutritional texts
among the fat-soluble vitamins, with vitamins A and E, in
contrast to the water-soluble vitamins B, C, and K. However,
discrepancies arose in explanations of apparent biological
activity exceeding expectations from measurements of contents
of fat-soluble vitamins. This discrepancy puzzled analysts
of breast-milk which, although inadequate for babies unless
supplemented by the action on the skin of sunlight, seemed
more biologically active than quantities in the fat in the
milk would elicit. Hydroxylations to the active hormonal forms
and metabolic conversions called conjugations cause transformations
changing the fat-soluble pro-hormone vitamin D into water-soluble
forms, active event to the point of toxicity; they are therefore
used cautiously for medical purposes.
Toxic effects of over-doses of vitamin D include excessive
absorption of calcium from the intestine and resorption from
the bone, which result in deposition of calcium and phosphorus
in soft tissues all over the body (calcinosis), with particular
damage to the heart, blood vessels, and kidneys (overdosing
is applied in dogs used as models in experimentation to raise
blood pressure). In extreme toxicity deposition of calcium
in lungs, tendons, and ligaments causes further damage and
symptoms such as lameness. Such problems have arisen from
excessive consumption—possibly unwitting—of fortified
foods or supplements.
The second of these remaining enigmas emerged from observations
on a disease complex in ruminants and horses resulting from
consumptions of certain plants, which is characterized by
excessive calcification of soft tissues.(See our the second
of our Case Studies The prevalence of the disease in cattle
varies from 10% to as high as 50% in areas of Argentina, Brazil,
Papua-New Guinea, Jamaica, and Hawaii; it can cause mortality
up to 60%. It affects about 17% of the sheep in southern Brazil
and in parts of India. It is unknown or rare in other areas
(e.g. Australia, Israel, and South Africa). In Europe the
problem occurs in Alpine regions; its colloquial veterinary
name of Manchester wasting disease poses another puzzle.
The trouble was traced to certain plants, at least as a predominant
factor. With interest increasing in the environment and organic
methods these considerations achieve extra significance for
farmers. Such plants are Cestrum diurnum (wild jasmine, day-blooming
jasmine, king-of-the-day), Trisetum flavescens (golden oats
or yellow oat grass), Nierembergia veitehii, Solanum esuriale,
S. torvum, and S. malacoxylon (glaucophyllum). The disease,
resulting from hypercalcemia and excessive production in the
thyroid of the hormone calcitonin, causes much distress and
presents severe problems in animal welfare.
We can find no evidence that our forebears or herbalists
had recourse to these sources for dietary intakes or for remedies
of vitamin D deficiency. It is possible that the high potency
and unpalatable factors put off or scared our ancestors off
utilization of these plants. They deserve at least appropriate
inclusion in the collections in the biomes of the Eden project
and remind us that botany still has enigmas to explain. A
plant equipped to produce compounds in the “animal”
D3 series is one thing, but with the genetics to furnish the
means of hydroxylations regarded for years as specific for
the organs of animals is another. Plant biologists and geneticists
are offered good subjects for research, deductions on evolution,
and prospects for applications.
Denouement
For veggies, people with skins sensitive to sunlight or who
don’t eat liver or fish, or for the housebound unable
to spend a few hours out-of-doors on fine winter days, VEGA
offers this advice to eke out the benefits of their summer
sunny delights. Upping altitude and downing latitude is one
way of extending the sun’s beneficence. Winter skiing
and cruising come expensive; however, a good cereal and fruit
breakfast with 3 or 4 slices of bread or toast through the
day “buttered” with a fortified dairy-free spread
and a cupful (250 ml) of plant milk used on the cereal or
in coffee or tea nicely supply essential requirements of vitamin
D during the bleak midwinter. These recommendations would
furnish about 5 mcg (200 IU) a day, divided equally between
the two sources, and satisfy most requirements; they could
be increased (e.g. by doubling or trebling) without harm and
relied on all the year if exposure to the sun is restricted,
especially at the higher latitudes of northern Europe.
Consumers need to check the labels of these products for
nutritional confirmation. Supplementation with calcium should
be balanced with increased intakes of vitamin D, preferably
with guidance from a doctor. Weight-bearing play, exercise,
or other activity should remain a year-round habit to strengthen
bones and gain some benefit from the light outdoors. Fluorescent
(tube) lighting indoors contributes a little to the formation
of vitamin D and more than the gain from tungsten filament
lamps. Dogs, cats, and budgies need their vitamin D too, with
adjustments for their different diets and exposure to the
sun.
<<
PAGE TOP >>
|
|
