Edited and updated 12-6-2010
A commonly seen comment is that we should be careful with vitamin D supplements to avoid overdoses. I found a reference in Mader's "Reptile Medicine and Surgery" that gives us a guideline for the dosage. (Please note that Mader is clear about this being a guideline, not the result of careful research!)
The target range is 200-2000 International Units (IU) per kilogram of tortoise a day. That would be roughly 100-1000 IU per pound for those who do not understand that metric is the superior system for this sort of thing
.
(Note- for the purposes of this article, figure that a kilogram, or 1000 grams is about 2 pounds, and 100 grams is about 3.5 ounces)
The danger zone is about 5000 IU/kg) a day. Overdoses can have nasty consequences, but to hit the danger zone, you would really have to work at it- although something like a high-dose vitamin D table for a very young tortoise would probably do it. The main symptoms of an overdose are hard to see and include things like calcification of soft tissues.
I cannot figure the dosage you get from the sun because there are far too many variables, but if your tortoise has free access to sunlight strong enough to give you a good tan, then you don't need to worry about this. If you live so far north that it is hard to tan in the winter, you may need to supplement with either UVB light or vitamins.
UVB light is a HUGE question mark right now- what is the best way to offer general UVA for vision and behaviors, and UVB-295nm range for D3 fabrication? Heck if I know. I would suggest that if you are using UVB lighting in your set-up (and you should, for several reasons), then you may STILL want to offer some supplemental vitamin D, but probably at the lower dosage end.
Most reptile products are oddly quiet about the dosages in their products, but some numbers I can find for common sources are:
IU's of Vitamin D in 100 grams of food:
- Cod liver oil- 8840 IU (or about 74 IU per drop, but may also be high in mercury)
- Fresh mushrooms- 14 IU
- Fresh mushrooms exposed to UV- 500 IU (note that this is vitamin D2, a less potent or effective version of the vitamin. It may only count as about 1/4th to 1/3rd as useful)
- Mazuri Tortoise Diet- 299 IU
- Canned tuna in oil- 235 IU
- Beef liver- 15 IU
Some other options are-
- Whole egg- about 20 IU in a medium egg
- One a Day Vitamin Tablets- 400 IU per tablet, or about 10-40 IU in a pinch of a crushed tablet (a common serving size for tortoises)
- Reptical with D3- 13.7 IU per gram of powder
Comments about 'forest-dwelling tortoises get all the D they need in the diet' are obviously inaccurate- unless there is a wild source of D that we do not know about. A half-pound (500gram) tortoise would need to eat the equivalent of 2 pounds of beef liver a day to get the recommended dose of D in the diet! (Granted, some Hinge-backs eat fish, and all forest species eat some mushrooms, but enough to completely satisfy the dose. There is also a lot of solar UV hitting them as well that close to the equator.)
Some vitamins are washed out of the body daily and need constant replenishment- B, C, K, etc. Vitamins A, D, and E are stored in the fat and used as needed. Since they are needed every day by a growing or active tortoise, we do not want the fat reserves to get too low, so need to help ensure an on-going dosage.
(Note that the flip side of this is that the tortoise needs a healthy amount of body fat to store energy in as well! A good argument for making sure they get enough food.)
As you think about vitamin D supplements, remember that 'wet' is better than 'dry'. Vitamin D in powder or dry tablet form is less effective than it is in actual food or in a oil base, like gel-caps. Some sources even suggest that 'dry' D does not count. The supplements in Mazuri, cat food, etc. are often stored in a oily base, but they will loose effectiveness over time, which is one reason for expiration dates on them.
DOSAGE SUGGESTION:
I think the most convenient version would be liquid vitamin D, which comes in 500 IU to 5000 IU strengths, usually taking 5 drops to accomplish. This lets you drizzle it fairly easily over the meal.
For the dosing, I would aim for-
- 1000 IU per kilogram for tortoises without supplemental UVB
- 500 IU per kilogram for tortoises with UVB lighting
BOTTOM LINE:
A good balance of calcium and D (and, of course, some other stuff) are vital to a tortoises health, especially in the early years. There is no reason to be afraid to offer supplemental calcium and vitamin D to give our tortoises the best chances for success.
Like any good thing, you can go too far. If you are giving a tiny tortoise an entire high-dose (2000 IU) D gel cap every day, you may be overdoing it. Short of that, we should be OK.
SOURCES:
Vitamin D in Wikipedia
Dr. Douglas Mader's "Reptile Medicine and Surgery"
www.uvguide.co.uk
and a note of thanks to EgyptianDan for the inspiration!
A commonly seen comment is that we should be careful with vitamin D supplements to avoid overdoses. I found a reference in Mader's "Reptile Medicine and Surgery" that gives us a guideline for the dosage. (Please note that Mader is clear about this being a guideline, not the result of careful research!)
The target range is 200-2000 International Units (IU) per kilogram of tortoise a day. That would be roughly 100-1000 IU per pound for those who do not understand that metric is the superior system for this sort of thing
.(Note- for the purposes of this article, figure that a kilogram, or 1000 grams is about 2 pounds, and 100 grams is about 3.5 ounces)
The danger zone is about 5000 IU/kg) a day. Overdoses can have nasty consequences, but to hit the danger zone, you would really have to work at it- although something like a high-dose vitamin D table for a very young tortoise would probably do it. The main symptoms of an overdose are hard to see and include things like calcification of soft tissues.
I cannot figure the dosage you get from the sun because there are far too many variables, but if your tortoise has free access to sunlight strong enough to give you a good tan, then you don't need to worry about this. If you live so far north that it is hard to tan in the winter, you may need to supplement with either UVB light or vitamins.
UVB light is a HUGE question mark right now- what is the best way to offer general UVA for vision and behaviors, and UVB-295nm range for D3 fabrication? Heck if I know. I would suggest that if you are using UVB lighting in your set-up (and you should, for several reasons), then you may STILL want to offer some supplemental vitamin D, but probably at the lower dosage end.
Most reptile products are oddly quiet about the dosages in their products, but some numbers I can find for common sources are:
IU's of Vitamin D in 100 grams of food:
- Cod liver oil- 8840 IU (or about 74 IU per drop, but may also be high in mercury)
- Fresh mushrooms- 14 IU
- Fresh mushrooms exposed to UV- 500 IU (note that this is vitamin D2, a less potent or effective version of the vitamin. It may only count as about 1/4th to 1/3rd as useful)
- Mazuri Tortoise Diet- 299 IU
- Canned tuna in oil- 235 IU
- Beef liver- 15 IU
Some other options are-
- Whole egg- about 20 IU in a medium egg
- One a Day Vitamin Tablets- 400 IU per tablet, or about 10-40 IU in a pinch of a crushed tablet (a common serving size for tortoises)
- Reptical with D3- 13.7 IU per gram of powder
Comments about 'forest-dwelling tortoises get all the D they need in the diet' are obviously inaccurate- unless there is a wild source of D that we do not know about. A half-pound (500gram) tortoise would need to eat the equivalent of 2 pounds of beef liver a day to get the recommended dose of D in the diet! (Granted, some Hinge-backs eat fish, and all forest species eat some mushrooms, but enough to completely satisfy the dose. There is also a lot of solar UV hitting them as well that close to the equator.)
Some vitamins are washed out of the body daily and need constant replenishment- B, C, K, etc. Vitamins A, D, and E are stored in the fat and used as needed. Since they are needed every day by a growing or active tortoise, we do not want the fat reserves to get too low, so need to help ensure an on-going dosage.
(Note that the flip side of this is that the tortoise needs a healthy amount of body fat to store energy in as well! A good argument for making sure they get enough food.)
As you think about vitamin D supplements, remember that 'wet' is better than 'dry'. Vitamin D in powder or dry tablet form is less effective than it is in actual food or in a oil base, like gel-caps. Some sources even suggest that 'dry' D does not count. The supplements in Mazuri, cat food, etc. are often stored in a oily base, but they will loose effectiveness over time, which is one reason for expiration dates on them.
DOSAGE SUGGESTION:
I think the most convenient version would be liquid vitamin D, which comes in 500 IU to 5000 IU strengths, usually taking 5 drops to accomplish. This lets you drizzle it fairly easily over the meal.
For the dosing, I would aim for-
- 1000 IU per kilogram for tortoises without supplemental UVB
- 500 IU per kilogram for tortoises with UVB lighting
BOTTOM LINE:
A good balance of calcium and D (and, of course, some other stuff) are vital to a tortoises health, especially in the early years. There is no reason to be afraid to offer supplemental calcium and vitamin D to give our tortoises the best chances for success.
Like any good thing, you can go too far. If you are giving a tiny tortoise an entire high-dose (2000 IU) D gel cap every day, you may be overdoing it. Short of that, we should be OK.
SOURCES:
Vitamin D in Wikipedia
Dr. Douglas Mader's "Reptile Medicine and Surgery"
www.uvguide.co.uk
and a note of thanks to EgyptianDan for the inspiration!
