Changes

==Why is it Important?==

==Why is it Important?==

Iodine is [[Nutrition Glossary#Essential Nutrients|essential]] because it is a major constituent of the '''thyroid hormones''' thyroxine (T₄) and 3,5,3’-triiodothyronine (T₃), the latter being considered the active form of the hormone.

Iodine is [[Nutrition Glossary#Essential Nutrients|essential]] because it is a major constituent of the [[Thyroid Gland - Anatomy & Physiology#Thyroid Hormone Physiology|'''thyroid hormones''']] thyroxine (T₄) and 3,5,3’-triiodothyronine (T₃), the latter being considered the active form of the hormone.

==Roles in the Body==

==Roles in the Body==

[[Thyroid Gland - Anatomy & Physiology#Thyroid Hormone Actions|Thyroid hormone]] is crucial for the regulation of cell activity, growth and development in growing animals and for the regulation of metabolic rate in adult animals. This means that iodine is an essential component for intermediary metabolism, reproduction and thermoregulation. Between 70-80% of total body iodine is concentrated in the [[Thyroid Gland - Anatomy & Physiology|thyroid gland]], the remainder is present in blood. Iodine is absorbed primarily as the iodide from the gastrointestinal tract and then distributed throughout the body. In the thyroid iodine is converted by a series of reactions to T₄ and T₃, which effectively represent the active biological forms of iodine. Iodine is also concentrated in the [[Renal Anatomy - Anatomy & Physiology|kidneys]] and the main route of excretion is via the kidneys in the urine.

[[Thyroid Gland - Anatomy & Physiology#Thyroid Hormone Actions|Thyroid hormone]] is crucial for the regulation of cell activity, growth and development in growing animals and for the regulation of metabolic rate in adult animals. This means that iodine is an essential component for intermediary metabolism, reproduction and [[Thermoregulation - Anatomy & Physiology|thermoregulation]]. Between 70-80% of total body iodine is concentrated in the [[Thyroid Gland - Anatomy & Physiology|thyroid gland]], the remainder is present in blood. Iodine is absorbed primarily as the iodide from the [[Alimentary System Overview - Anatomy & Physiology|gastrointestinal tract]] and then distributed throughout the body. In the thyroid, iodine is converted by a series of reactions to T₄ and T₃, which effectively represent the active biological forms of iodine. Iodine is also concentrated in the [[Renal Anatomy - Anatomy & Physiology|kidneys]] and the main route of excretion is via the kidneys in the urine.

==Consequences of Iodine Deficiency==

==Consequences of Iodine Deficiency==

#'''Thyroid changes''': In a long-term feeding trial of dogs receiving low dietary levels of iodine (0.3 mg/kg dry matter – DM), thyroid glands became hyperplastic and hypertrophic during the first 9 months. Significant increases in the thyroid uptake of radiolabelled iodine were also reported<ref>Norris, C, Fritz, T, Taylor, J (1970). “Cycle of accommodation to restricted dietary iodide in thyroid gland of the beagle dog”. Am. J. Vet. Res. 31:21-33.</ref>. However, the dogs seemed to adapt as the study progressed beyond 9 months because the thyroid glands eventually returned to normal size and appearance.

#'''Thyroid changes''': In a long-term feeding trial of dogs receiving low dietary levels of iodine (0.3 mg/kg dry matter – DM), thyroid glands became hyperplastic and hypertrophic during the first 9 months. Significant increases in the thyroid uptake of radiolabelled iodine were also reported<ref>Norris, C, Fritz, T, Taylor, J (1970). “Cycle of accommodation to restricted dietary iodide in thyroid gland of the beagle dog”. Am. J. Vet. Res. 31:21-33.</ref>. However, the dogs seemed to adapt as the study progressed beyond 9 months because the thyroid glands eventually returned to normal size and appearance.

#'''Serum levels of thyroid hormones''': When adult beagles were fed very low intakes of iodine (50 or 20 µg/day, equivalent to a dietary iodine content of about 0.27 and 0.11 mg/kg DM respectively) marked reductions in serum T₄ but not T₃ were observed<ref>Belshaw, BE, Cooper TB, Becker Jr. DV (1975). “The iodine requirement and influence of iodine intake on iodine metabolism and thyroid function in the adult beagle”. Endocrinology 96:1280-1291.</ref>.

#'''Serum levels of thyroid hormones''': When adult beagles were fed very low intakes of iodine (50 or 20 µg/day, equivalent to a dietary iodine content of about 0.27 and 0.11 mg/kg DM respectively) marked reductions in serum T₄ but not T₃ were observed<ref>Belshaw, BE, Cooper TB, Becker Jr. DV (1975). “The iodine requirement and influence of iodine intake on iodine metabolism and thyroid function in the adult beagle”. Endocrinology 96:1280-1291.</ref>.

#'''[[Goitre]] and other clinical signs''': In dogs fed low iodine levels primarily as a result of receiving an all-meat diet, signs consisted of goitre (enlargement of the thyroid gland), weight gain and adverse effects on hair condition<ref>Thompson, T (1979). “Iodine-deficiency goitre in a bitch”. New Zealand Vet. J. 27:113.</ref><ref>Nuttall, W (1986). “Iodine deficiency in working dogs”. New Zealand Vet. J. 34:72.</ref>.  

#'''[[Goitre]] and other clinical signs''': In dogs fed low iodine levels primarily as a result of receiving an all-meat diet, signs consisted of goitre (enlargement of the thyroid gland), weight gain and adverse effects on [[HAir - Anatomy & Physiology|hair]] condition<ref>Thompson, T (1979). “Iodine-deficiency goitre in a bitch”. New Zealand Vet. J. 27:113.</ref><ref>Nuttall, W (1986). “Iodine deficiency in working dogs”. New Zealand Vet. J. 34:72.</ref>.  

====Cat:====  

====Cat:====  

There is little information on iodine deficiency in the cat but one study identified changes to the thyroid gland linked to a low iodine diet.

There is little information on iodine deficiency in the cat but one study identified changes to the thyroid gland linked to a low iodine diet.

==Toxicity==

==Toxicity==

There are various clinical signs associated with excessive iodine intake including changes to the skin and hair, and bone abnormalities. [[Goitre]] – normally a feature of chronic iodine deficiency – may also occur because the prolonged intake of excessive iodine levels increases plasma iodine, which in turn has a negative effect on iodine uptake by the thyroid gland. In general, observations in dogs and cats are restricted to more subtle effects.   

There are various clinical signs associated with excessive iodine intake including changes to the [[Skin - Anatomy & Physiology|skin]] and hair, and [[Bones - Anatomy & Physiology|bone]] abnormalities. [[Goitre]] – normally a feature of chronic iodine deficiency – may also occur because the prolonged intake of excessive iodine levels increases plasma iodine, which in turn has a negative effect on iodine uptake by the thyroid gland. In general, observations in dogs and cats are restricted to more subtle effects.   

====Dog:====  

====Dog:====  

When dogs were given a single dose of potassium iodate delivering 100 mg iodine/kg bodyweight (BW) it caused anorexia and occasional [[Vomiting|vomiting]]. Higher doses of 200 and 250 mg iodine/kg BW caused '''anorexia, coma and death'''<ref>Webster, SH, Stohlman, EF, Highman, B (1966). “The toxicology of potassium and sodium iodates. III. Acute and subacute oral toxicology of potassium iodate in dogs”. Toxicol. Appl. Pharmacol. 8:185-192.</ref>. A lower (but still high) intake of iodine of 775 µg/kg BW/day in puppies was associated with bone abnormalities. This intake is equivalent to a dietary iodine content of about 17-18 mg/kg DM<ref>Castillo, V, Pisarev, M, Lalia, J, Junco, M, Rodriguez, M, Cabrin, R, Marquez, A (2001). “Commercial diet induced hypothyroidism due to high iodine.  A histological and radiological analysis”. Vet. Quart. 23:218-223.</ref>.

When dogs were given a single dose of potassium iodate delivering 100 mg iodine/kg bodyweight (BW) it caused anorexia and occasional [[Vomiting|vomiting]]. Higher doses of 200 and 250 mg iodine/kg BW caused '''anorexia, coma and death'''<ref>Webster, SH, Stohlman, EF, Highman, B (1966). “The toxicology of potassium and sodium iodates. III. Acute and subacute oral toxicology of potassium iodate in dogs”. Toxicol. Appl. Pharmacol. 8:185-192.</ref>. A lower (but still high) intake of iodine of 775 µg/kg BW/day in puppies was associated with bone abnormalities. This intake is equivalent to a dietary iodine content of about 17-18 mg/kg DM<ref>Castillo, V, Pisarev, M, Lalia, J, Junco, M, Rodriguez, M, Cabrin, R, Marquez, A (2001). “Commercial diet induced hypothyroidism due to high iodine.  A histological and radiological analysis”. Vet. Quart. 23:218-223.</ref>.

====Cat:====  

====Cat:====  

There are conflicting reports of the effects of excessive iodine in cats. For example, Kyle et al. fed a diet containing an iodine content of 21 mg/kg DM to cats for 5 months and observed no clinical abnormalities or changes in serum free thyroxine levels<ref>Kyle, A, Tartellin, MF, Cooke, R, Ford, HC (1994). “Serum free thyroxine levels in cats maintained on diets relatively high or low in iodine”. New Zealand Vet. J. 42:101-103.</ref>. In contrast, another study reported a significant depression in serum free thyroxine when cats were fed a dietary iodine level of 13.8 mg/kg DM for only two weeks<ref>Tartellin, MF, Ford, HC (1994). “Dietary iodine level and thyroid function in the cat”. J Nutr. 124:2577S-2578S.</ref>. Perhaps this was a temporary effect that eventually would have reverted to normal. It has also been suggested that excessive dietary iodine is a potential cause of feline hyperthyroidism but epidemiological studies have yet to identify a causal relationship<ref>Scarlett, JM (1994). “Epidemiology of thyroid diseases of dogs and cats”. Vet. Clin. North Am: Small Anim. Pract. 24:477-486.</ref>.

There are conflicting reports of the effects of excessive iodine in cats. For example, Kyle ''et al.'' fed a diet containing an iodine content of 21 mg/kg DM to cats for 5 months and observed no clinical abnormalities or changes in serum free thyroxine levels<ref>Kyle, A, Tartellin, MF, Cooke, R, Ford, HC (1994). “Serum free thyroxine levels in cats maintained on diets relatively high or low in iodine”. New Zealand Vet. J. 42:101-103.</ref>. In contrast, another study reported a significant depression in serum free thyroxine when cats were fed a dietary iodine level of 13.8 mg/kg DM for only two weeks<ref>Tartellin, MF, Ford, HC (1994). “Dietary iodine level and thyroid function in the cat”. J Nutr. 124:2577S-2578S.</ref>. Perhaps this was a temporary effect that eventually would have reverted to normal. It has also been suggested that excessive dietary iodine is a potential cause of feline [[hyperthyroidism]] but epidemiological studies have yet to identify a causal relationship<ref>Scarlett, JM (1994). “Epidemiology of thyroid diseases of dogs and cats”. Vet. Clin. North Am: Small Anim. Pract. 24:477-486.</ref>.

==Dietary Sources==

==Dietary Sources==

Iodine is widely distributed in nature but in very small amounts and with large variations. The iodine content of crops depends on the iodine level in the soil. Soils particularly low in iodine are often designated as goitre regions where forages have to be supplemented with iodine to provide an adequate diet. Protein sources of marine origin are generally good sources and oilseed proteins and concentrates contain reasonable amounts. To ensure adequate dietary contents, dog and cat foods are usually supplemented with inorganic iodine salts such as potassium iodide and calcium iodate.

Iodine is widely distributed in nature but in very small amounts and with large variations. The iodine content of crops depends on the iodine level in the soil. Soils particularly low in iodine are often designated as goitre regions where forages have to be supplemented with iodine to provide an adequate diet. [[Protein - Nutrition|Protein]] sources of marine origin are generally good sources and oilseed proteins and concentrates contain reasonable amounts. To ensure adequate dietary contents, dog and cat foods are usually supplemented with inorganic iodine salts such as potassium iodide and calcium iodate.

==References==

==References==

[[Category:Minerals in Nutrition]]

[[Category:Minerals in Nutrition]]

[[Category:To Do - Nutrition]]

[[Category:To Do - Nutrition]]

[[Category:To Do - Nutrition preMars]]

[[Category:To Do - Batch 2]]